gdb/reverse: Fix recording vmov[u|a]p[s|d] instructions

gdb/reverse: Fix recording vmov[u|a]p[s|d] instructions

Tom de Vries reported that some of the test for the vmov[u|a]p[s|d] were
failing. In my machine xmm3 was consistently set to 0x54, but apparently
that is different depending on the system. This commit zeroes out xmm3
at the start of the test instead.

While debugging the test failures, I also noticed an issue where the
recording wasn't saving all the required memory. That happened because
vmovs[s|d] shares its opcode with vmovap[s|d], meaning they seem to
share code paths, but the latter encodes memory modification size on
VEX.L whereas the former encodes in VEX.pp. So this commit fixed that,
and made the relevant tests more robust and complete.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32561
Approved-By: Guinevere Larsen <guinevere@redhat.com>