x86, microcode, amd: Fix warnings and errors on with CONFIG_MICROCODE=m

Fix section mismatch warnings on microcode_amd_early.
Compile error occurs when CONFIG_MICROCODE=m, change so that early
loading depends on microcode_core.

Reported-by: Yinghai Lu <yinghai@kernel.org>
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Jacob Shin <jacob.shin@amd.com>
Link: http://lkml.kernel.org/r/20130531150241.GA12006@jshin-Toonie
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>