cmd/asm/internal/asm: add extra AVX-512 tests

These tests were meant to be included into https://golang.org/cl/113315,
but were lost somewhere in the middle.

This CL adds hand-written AVX-512 tests that complement
auto-generated test suite.

It's worth including it, because:

	- It covers every new Z-case explicitly
	- Does checks every opcode suffix encoding

Change-Id: Id6da5f58773e07bef3d532fc3ca5db391d380ebf
Reviewed-on: https://go-review.googlesource.com/115858
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>