x86: correct ISA-used version recording

Updating should be based solely on the current instruction. For example,
recording of VEX-encoded insns as v3 should be independent of there
being earlier AMX insns.

Further for BASELINE only a very limited set of the
GNU_PROPERTY_X86_FEATURE_2_* bits should actually be taken into account:
Most of the bits represent advanced (later) features (XSAVE, XSAVEOPT,
and XSAVEC for example being part of v3).