cpu: add DIT option and hwcap DIT support

Follow-up to https://go.dev/cl/597377, add a option for DIT so it can be
set via GODEBUG, and add hwcap support for Linux.

Change-Id: Ib094b520edea9c099d37f121b09d02b31644a433
Reviewed-on: https://go-review.googlesource.com/c/sys/+/598719
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

cpu/cpu_arm64.go

@@ -38,6 +38,7 @@ func initOptions() {
 		{Name: "dcpop", Feature: &ARM64.HasDCPOP},
 		{Name: "asimddp", Feature: &ARM64.HasASIMDDP},
 		{Name: "asimdfhm", Feature: &ARM64.HasASIMDFHM},
+		{Name: "dit", Feature: &ARM64.HasDIT},
 	}
 }
 

cpu/cpu_linux_arm64.go

@@ -35,6 +35,7 @@ const (
 	hwcap_SHA512   = 1 << 21
 	hwcap_SVE      = 1 << 22
 	hwcap_ASIMDFHM = 1 << 23
+	hwcap_DIT      = 1 << 24
 
 	hwcap2_SVE2 = 1 << 1
 )
@@ -106,6 +107,8 @@ func doinit() {
 	ARM64.HasSHA512 = isSet(hwCap, hwcap_SHA512)
 	ARM64.HasSVE = isSet(hwCap, hwcap_SVE)
 	ARM64.HasASIMDFHM = isSet(hwCap, hwcap_ASIMDFHM)
+	ARM64.HasDIT = isSet(hwCap, hwcap_DIT)
+
 
 	// HWCAP2 feature bits
 	ARM64.HasSVE2 = isSet(hwCap2, hwcap2_SVE2)