cmd/asm: uncomment tests for PCMPESTRI, PHMINPOSUW

cmd/asm: uncomment tests for PCMPESTRI, PHMINPOSUW

Instructions are implemented in the following revisions:
PCMPESTRI - https://golang.org/cl/22337
PHMINPOSUW - https://golang.org/cl/18853

It is unknown when x86test will be updated/re-run, but tests are useful
to check which x86 instructions are not yet supported.
As an example of tool that uses this information, there is Damien
Lespiau x86db.

Part of the mission to add missing amd64 SSE4 instructions to Go asm.

Change-Id: I512ff26040f47a0976b3e37000fb1f37eac5b762
Reviewed-on: https://go-review.googlesource.com/55830
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>