vendor x/sys/cpu and update x/crypto/blake2b (#5870)

This change updates the vendor'd x/crypto/blake2b package and
adds x/sys/cpu.

This change fixes an issue for Go1.11 affecting x/crypto/blake2b
since G1.11 removes the runtime-internal functions `suports_avx()` and
`supports_avx2()`.

vendor/golang.org/x/crypto/blake2b/blake2b_amd64.s

@@ -279,12 +279,3 @@ noinc:
 
 	MOVQ BP, SP
 	RET
-
-// func supportsSSE4() bool
-TEXT ·supportsSSE4(SB), 4, $0-1
-	MOVL $1, AX
-	CPUID
-	SHRL $19, CX  // Bit 19 indicates SSE4 support
-	ANDL $1, CX  // CX != 0 if support SSE4
-	MOVB CX, ret+0(FP)
-	RET