feat(s/c/aes): internal/cpu => internal/cpuproxy

I extracted this diff from 62177de with
the intent of coming up with a more manageable patch set.

The idea here is to take advantage of the cpuproxy package to use the
information it provides to better initialize crypto using arm64.

The original issue describing this problem in its full extent was
ooni/probe#1444.

We're now working to forward-port this patch to go1.17.

The current issue describing this problem as of go1.17 is
ooni/probe#1863.

Is there a better way?

src/crypto/aes/cipher_asm.go

@@ -10,7 +10,7 @@ package aes
 import (
 	"crypto/cipher"
 	"crypto/internal/subtle"
-	"internal/cpu"
+	"internal/cpuproxy"
 )
 
 // defined in asm_*.s
@@ -28,8 +28,8 @@ type aesCipherAsm struct {
 	aesCipher
 }
 
-var supportsAES = cpu.X86.HasAES || cpu.ARM64.HasAES
-var supportsGFMUL = cpu.X86.HasPCLMULQDQ || cpu.ARM64.HasPMULL
+var supportsAES = cpuproxy.HasAES()
+var supportsGFMUL = cpuproxy.HasGFMUL()
 
 func newCipher(key []byte) (cipher.Block, error) {
 	if !supportsAES {