RISC-V: Move register name file initialization

This is (a) to group per-option register name file initialization
together with Zfinx handling and (b) to prepare future RV32E handling.

opcodes/ChangeLog:

	* riscv-dis.c (set_default_riscv_dis_options): Move setting
	actual register names to init_dis_per_arch_and_options.
	(parse_riscv_dis_option_without_args): Likewise.
	(init_dis_per_arch_and_options): Set register names when the
	architecture or an option is changed.

opcodes/riscv-dis.c

@@ -65,12 +65,14 @@ static const char * const *riscv_fpr_names;
 /* If set, disassemble as most general instruction.  */
 static bool no_aliases = false;
 
+/* If set, disassemble with numeric registers.  */
+static bool is_numeric = false;
+
 static void
 set_default_riscv_dis_options (void)
 {
-  riscv_gpr_names = riscv_gpr_names_abi;
-  riscv_fpr_names = riscv_fpr_names_abi;
   no_aliases = false;
+  is_numeric = false;
 }
 
 static bool
@@ -79,10 +81,7 @@ parse_riscv_dis_option_without_args (const char *option)
   if (strcmp (option, "no-aliases") == 0)
     no_aliases = true;
   else if (strcmp (option, "numeric") == 0)
-    {
-      riscv_gpr_names = riscv_gpr_names_numeric;
-      riscv_fpr_names = riscv_fpr_names_numeric;
-    }
+    is_numeric = true;
   else
     return false;
   return true;
@@ -174,6 +173,8 @@ init_dis_per_arch (void)
 static void
 init_dis_per_arch_and_options (void)
 {
+  riscv_gpr_names = is_numeric ? riscv_gpr_names_numeric : riscv_gpr_names_abi;
+  riscv_fpr_names = is_numeric ? riscv_fpr_names_numeric : riscv_fpr_names_abi;
   /* If arch has Zfinx extension, use GPR to disassemble.  */
   if (riscv_subset_supports (&riscv_rps_dis, "zfinx"))
     riscv_fpr_names = riscv_gpr_names;