x86-microcode: generic interface refactoring

This is the 1st patch in the series. Here the aim was to avoid any
significant changes, logically-wise.

So it's mainly about generic interface refactoring: e.g. make
microcode_{intel,amd}.c more about arch-specific details and less
about policies like make-sure-we-run-on-a-target-cpu
(no more set_cpus_allowed_ptr() here) and generic synchronization (no
more microcode_mutex here).

All in all, more line have been deleted than added.

4 files changed, 145 insertions(+), 198 deletions(-)

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>