gdb/record: support AVX instructions VMOVDQ(U|A) when recording

gdb/record: support AVX instructions VMOVDQ(U|A) when recording

This commit adds support for the instructions VMOVDQU and VMOVDQA, used
to move values to/from 256 bit registers. Unfortunately, the
programmer's manual is very incomplete (if not wrong) about these
instructions, so the logic had to be reverse engineered from how gcc
actually encodes the instruction.

This commit also changes the memory regions from the test to store 256
bits, so its easier to test the instructions and that we're recording
ymm registers correctly.

Approved-By: Tom Tromey <tom@tromey.com>