[PATCH 0/3] x86: improve encoding selection and prereq tidying

[Jan Beulich]

While perhaps seemingly unrelated, the first two changes here are
kind of fallout from preparing the 3rd patch. That 3rd patch also
depends on the earlier submitted "x86: fold certain VEX and EVEX
templates", at least for its use of need_evex_encoding(). The
first two patches should be pretty much independent of the earlier
series.

1: correct cpu_arch_isa_flags maintenance
2: drop cpu_arch_tune_flags
3: prefer VEX encodings over EVEX ones when possible

Jan