internal/cpu: don't define CacheLinePadSize for mips64x
internal/cpu: don't define CacheLinePadSize for mips64x

For libgo the definition comes from the generated file cpugen.go.

Fixes https://gcc.gnu.org/PR98041

Change-Id: I355d09f88816821a7afff3c90a7c9e148edf10b3
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/273866
Trust: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend