[x86] Run clang-format

This converts a bunch of the old LK style to the newer style.

Change-Id: I0f9dfc6b2b9b30b7630dc1e2271e8da815edd1d8

[kernel][x86] add support for clflush/clflushopt for cache ops

-Cache clean operations aren't done much on x86, but in the few places
they are, using clflush is a massive win.
-Informal benchmarking with 'k cache_tests' seem to indicate that trying
to micro optimize the feature bit detection is barely measurable, so
go ahead and do it the simple way for now.

Change-Id: Ie178cdd01d143f1f2676219105136eb87223c474

[x86] Add serializing instruction to arch_sync_cache_range

This is in line with Intel's recommendations for self-modifying code.
It will ensure visibility of changes to the instruction stream.

Change-Id: I5bbc1ab66319d3df5303d890483604c930e5cc1b

[kernel][x86] brute force rename arch/x86/* files from .c to .cpp

Change-Id: I8ec0a28f71a7d4d3eba4f022873e59dbbbd0bd1e