cpu: add linux/ppc64x

Port from Go internal/cpu.

Fixes golang/go#25185

Change-Id: Id3cac18da6ffec9d10df755c4032ce3068ab634d
Reviewed-on: https://go-review.googlesource.com/c/152938
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cpu/cpu_ppc64x.go

@@ -8,4 +8,25 @@ package cpu
 
 const cacheLineSize = 128
 
-func doinit() {}
+// HWCAP/HWCAP2 bits. These are exposed by the kernel.
+const (
+	// ISA Level
+	_PPC_FEATURE2_ARCH_2_07 = 0x80000000
+	_PPC_FEATURE2_ARCH_3_00 = 0x00800000
+
+	// CPU features
+	_PPC_FEATURE2_DARN = 0x00200000
+	_PPC_FEATURE2_SCV  = 0x00100000
+)
+
+func doinit() {
+	// HWCAP2 feature bits
+	PPC64.IsPOWER8 = isSet(HWCap2, _PPC_FEATURE2_ARCH_2_07)
+	PPC64.IsPOWER9 = isSet(HWCap2, _PPC_FEATURE2_ARCH_3_00)
+	PPC64.HasDARN = isSet(HWCap2, _PPC_FEATURE2_DARN)
+	PPC64.HasSCV = isSet(HWCap2, _PPC_FEATURE2_SCV)
+}
+
+func isSet(hwc uint, value uint) bool {
+	return hwc&value != 0
+}