gdb/record: Add recording support to vpbroadcast instructions

This commit adds recording support to all AVX and AVX2 instructions
of the form vpbroadcast. GDB is not yet concerned about AVX512 in
recording mode, so for now we only support the AVX2 registers and
instructions.

This commit also updates the gdb.reverse/i386-avx-reverse.exp to test
broadcast instructions.

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