x86: moved microcode.c to microcode_intel.c

Combine both generic and arch-specific parts of microcode into a
single module (arch-specific parts are config-dependent).

Also while we are at it, move arch-specific parts from microcode.h
into their respective arch-specific .c files.

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: "Peter Oruba" <peter.oruba@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>