x86, microcode: fix symbol exports

fix tons of build errors:

 arch/x86/kernel/built-in.o: In function `microcode_fini_cpu':
 microcode_intel.c:(.text+0x11598): undefined reference to `microcode_mutex'
 microcode_intel.c:(.text+0x115a4): undefined reference to `ucode_cpu_info'
 microcode_intel.c:(.text+0x115ae): undefined reference to `ucode_cpu_info'
 microcode_intel.c:(.text+0x115bc): undefined reference to `microcode_mutex'
 [...]

Signed-off-by: Ingo Molnar <mingo@elte.hu>