x86/APX: legacy promoted insns can't access %xmm16-%xmm31

Irrespective of the encoding being EVEX, the usable SIMD register range
continues to be limited to %xmm0-%xmm15. Enforce this in gas (but
continue to generate code, as in principle we know how to encode
things) and recognize/flag the case in the disassembler.

Oddly enough wrong forms were actually used in the testsuite (register-
only forms are then really meaningless to test here, and are hence
dropped instead of adjusted).

Convert the POP2 test that needs touching anyway (due to a bad ModR/M
byte having been chosen) to .insn.
10 files changed