internal/cpu: add sha512 for arm64

The new M1 cpu (Apple) comes with sha512 hardware
acceleration feature.

Change-Id: I823d1e9b09b472bd21571eee75cc5314cd66b1ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/408836
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/internal/cpu/cpu.go

@@ -61,6 +61,7 @@ var ARM64 struct {
 	HasPMULL     bool
 	HasSHA1      bool
 	HasSHA2      bool
+	HasSHA512    bool
 	HasCRC32     bool
 	HasATOMICS   bool
 	HasCPUID     bool

src/internal/cpu/cpu_arm64.go

@@ -12,6 +12,7 @@ func doinit() {
 		{Name: "pmull", Feature: &ARM64.HasPMULL},
 		{Name: "sha1", Feature: &ARM64.HasSHA1},
 		{Name: "sha2", Feature: &ARM64.HasSHA2},
+		{Name: "sha512", Feature: &ARM64.HasSHA512},
 		{Name: "crc32", Feature: &ARM64.HasCRC32},
 		{Name: "atomics", Feature: &ARM64.HasATOMICS},
 		{Name: "cpuid", Feature: &ARM64.HasCPUID},

src/internal/cpu/cpu_arm64_darwin.go

@@ -9,6 +9,7 @@ package cpu
 func osInit() {
 	ARM64.HasATOMICS = sysctlEnabled([]byte("hw.optional.armv8_1_atomics\x00"))
 	ARM64.HasCRC32 = sysctlEnabled([]byte("hw.optional.armv8_crc32\x00"))
+	ARM64.HasSHA512 = sysctlEnabled([]byte("hw.optional.armv8_2_sha512\x00"))
 
 	// There are no hw.optional sysctl values for the below features on Mac OS 11.0
 	// to detect their supported state dynamically. Assume the CPU features that