runtime, internal/cpu: change cache line size for arm64 to 64 bytes

According to http://infocenter.arm.com:
* ARM Cortex-A53 (Raspberry Pi 3, Pine A64)
* ARM Cortex-A57 (Opteron A1100, Tegra X1)
* ARM Cortex-A72
all have a cache line size of 64 bytes.

Change-Id: I4b333e930792fb1a221b3ca6f395bfa1b7762afa
Reviewed-on: https://go-review.googlesource.com/43250
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/internal/cpu/cpu_arm64.go

@@ -4,4 +4,4 @@
 
 package cpu
 
-const CacheLineSize = 32
+const CacheLineSize = 64

src/runtime/internal/sys/arch_arm64.go

@@ -7,7 +7,7 @@ package sys
 const (
 	ArchFamily          = ARM64
 	BigEndian           = 0
-	CacheLineSize       = 32
+	CacheLineSize       = 64
 	DefaultPhysPageSize = 65536
 	PCQuantum           = 4
 	Int64Align          = 8