microcode: clean up microcode_resume_cpu

microcode: clean up microcode_resume_cpu

Previously, a per-cpu ucode cache is maintained. Then each CPU had one
per-cpu update cache and there might be multiple versions of microcode.
Thus microcode_resume_cpu tried best to update microcode by loading
every update cache until a successful load.

But now the cache struct is simplified a lot and only a single ucode is
cached. a single invocation of ->apply_microcode() would load the cache
and make microcode updated.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>