x86, microcode: Vendor abstract out save_microcode_in_initrd()

Currently save_microcode_in_initrd() is declared in vendor neutural
microcode.h file, but defined in vendor specific
microcode_intel_early.c file. Vendor abstract it out to
microcode_core_early.c with a wrapper function.

Signed-off-by: Jacob Shin <jacob.shin@amd.com>
Link: http://lkml.kernel.org/r/1369940959-2077-3-git-send-email-jacob.shin@amd.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>