RISC-V: Print using .dword on RV64

`riscv_disassemble_data' has an ability to print 8-byte data with .dword
but this is not utilized.  This is possibly because, XLEN was not set
before disassembling an instruction.

Since prerequisite commits now set XLEN in `riscv_get_disassembler', it's
now safe to use .dword on RV64.

gas/ChangeLog:

	* testsuite/gas/riscv/mapping-04b.d: Change to use RV64I.  Check
	that .dword is actually used.
	* testsuite/gas/riscv/mapping-norelax-04b.d: Likewise.
	* testsuite/gas/riscv/mapping-04b-32.d: New test, the same as
	mapping-04b except it uses RV32I and .dword should not be used.

opcodes/ChangeLog:

	* riscv-dis.c (riscv_data_length): Print using .dword on RV64.

gas/testsuite/gas/riscv/mapping-04b-32.d

@@ -0,0 +1,23 @@
+#as: -march=rv32i
+#source: mapping-04.s
+#objdump: -d
+
+.*:[ 	]+file format .*
+
+
+Disassembly of section .text:
+
+0+000 <.text>:
+[ 	]+0:[ 	]+00001001[ 	]+.word[ 	]+0x00001001
+[ 	]+4:[ 	]+00001001[ 	]+.word[ 	]+0x00001001
+[ 	]+8:[ 	]+00000001[ 	]+.word[ 	]+0x00000001
+[ 	]+c:[ 	]+00[ 	]+.byte[ 	]+0x00
+[ 	]+d:[ 	]+00000013[ 	]+nop
+[ 	]+11:[ 	]+00a50533[ 	]+add[ 	]+a0,a0,a0
+[ 	]+15:[ 	]+20022002[ 	]+.word[ 	]+0x20022002
+[ 	]+19:[ 	]+20022002[ 	]+.word[ 	]+0x20022002
+[ 	]+1d:[ 	]+2002[ 	]+.short[ 	]+0x2002
+[ 	]+1f:[ 	]+00b585b3[ 	]+add[ 	]+a1,a1,a1
+[ 	]+23:[ 	]+0000[ 	]+.2byte[ 	]+0x0
+[ 	]+25:[ 	]+0000[ 	]+.2byte[ 	]+0x0
+#...

gas/testsuite/gas/riscv/mapping-04b.d

@@ -1,4 +1,4 @@
-#as:
+#as: -march=rv64i
 #source: mapping-04.s
 #objdump: -d
 
@@ -8,14 +8,12 @@
 Disassembly of section .text:
 
 0+000 <.text>:
-[ 	]+0:[ 	]+00001001[ 	]+.word[ 	]+0x00001001
-[ 	]+4:[ 	]+00001001[ 	]+.word[ 	]+0x00001001
+[ 	]+0:[ 	]+0000100100001001[ 	]+.dword[ 	]+0x0000100100001001
 [ 	]+8:[ 	]+00000001[ 	]+.word[ 	]+0x00000001
 [ 	]+c:[ 	]+00[ 	]+.byte[ 	]+0x00
 [ 	]+d:[ 	]+00000013[ 	]+nop
 [ 	]+11:[ 	]+00a50533[ 	]+add[ 	]+a0,a0,a0
-[ 	]+15:[ 	]+20022002[ 	]+.word[ 	]+0x20022002
-[ 	]+19:[ 	]+20022002[ 	]+.word[ 	]+0x20022002
+[ 	]+15:[ 	]+2002200220022002[ 	]+.dword[ 	]+0x2002200220022002
 [ 	]+1d:[ 	]+2002[ 	]+.short[ 	]+0x2002
 [ 	]+1f:[ 	]+00b585b3[ 	]+add[ 	]+a1,a1,a1
 [ 	]+23:[ 	]+0000[ 	]+.2byte[ 	]+0x0

gas/testsuite/gas/riscv/mapping-norelax-04b.d

@@ -1,4 +1,4 @@
-#as: -mno-relax
+#as: -march=rv64i -mno-relax
 #source: mapping-04.s
 #objdump: -d
 
@@ -8,15 +8,13 @@
 Disassembly of section .text:
 
 0+000 <.text>:
-[ 	]+0:[ 	]+00001001[ 	]+.word[ 	]+0x00001001
-[ 	]+4:[ 	]+00001001[ 	]+.word[ 	]+0x00001001
+[ 	]+0:[ 	]+0000100100001001[ 	]+.dword[ 	]+0x0000100100001001
 [ 	]+8:[ 	]+00000001[ 	]+.word[ 	]+0x00000001
 [ 	]+c:[ 	]+00[ 	]+.byte[ 	]+0x00
 [ 	]+d:[ 	]+00[ 	]+.byte[ 	]+0x00
 [ 	]+e:[ 	]+0001[ 	]+.2byte[ 	]+0x1
 [ 	]+10:[ 	]+00a50533[ 	]+add[ 	]+a0,a0,a0
-[ 	]+14:[ 	]+20022002[ 	]+.word[ 	]+0x20022002
-[ 	]+18:[ 	]+20022002[ 	]+.word[ 	]+0x20022002
+[ 	]+14:[ 	]+2002200220022002[ 	]+.dword[ 	]+0x2002200220022002
 [ 	]+1c:[ 	]+2002[ 	]+.short[ 	]+0x2002
 [ 	]+1e:[ 	]+00b585b3[ 	]+add[ 	]+a1,a1,a1
 [ 	]+22:[ 	]+0001[ 	]+.2byte[ 	]+0x1

opcodes/riscv-dis.c

@@ -1000,7 +1000,7 @@ riscv_data_length (bfd_vma memaddr,
   bfd_vma length;
   bool found = false;
 
-  length = 4;
+  length = xlen > 32 ? 8 : 4;
   if (info->symtab_size != 0
       && bfd_asymbol_flavour (*info->symtab) == bfd_target_elf_flavour
       && last_map_symbol >= 0)
@@ -1027,7 +1027,14 @@ riscv_data_length (bfd_vma memaddr,
       offset -= memaddr;
       length = (offset < length) ? offset : length;
     }
-  length = length == 3 ? 2 : length;
+  static const bfd_vma aligned_length[] = {
+    /* [0..0] */ 0,
+    /* [1..1] */ 1,
+    /* [2..3] */ 2, 2,
+    /* [4..7] */ 4, 4, 4, 4,
+    /* [8..8] */ 8,
+  };
+  length = aligned_length[length];
   return length;
 }