gdb/record: support more AVX arithmetic instructions

gdb/record: support more AVX arithmetic instructions

This commit adds support to the following AVX/AVX2 instructions:
* VPADD[B|W|D|Q]
* VPMUL[LW|LD|HW|HUW|UDQ]
* VXORP[S|D]
* VPAND[|N]

This required some reworking on the loop that processes instruction
prefixes, because the opcode for VPMULLD overlapped with a valid
instruction prefix. To fix that, rather than using "goto out_prefixes",
this commit changes the infinite loop to only run while we don't find
another VEX prefix. That should be OK, as the intel manual (page 526 on
the March 2024 edition) says that the VEX prefix is always the last one.