[dev.simd] simd/_gen/simdgen, cmd/compile: add memory op machine ops
This CL adds the machine ops for memory-op and also their prog writing
logic.
This CL also fixes a bug in the XED parser. Previously the
merge of machine ops is not checking the CPU feature, so some AVX
instruction might have their "memFeatures" field set incorrectly.
However since that field is not used until this CL, putting the fix here
should be ok.
Change-Id: I91031cbbf63453257473dd1d2ff47f7496d1a01d
Reviewed-on: https://go-review.googlesource.com/c/go/+/701198
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com>