x86, microcode, AMD: Add reverse equiv table search

We search the equivalence table using the CPUID(1) signature of the
CPU in order to get the equivalence ID of the patch which we need to
apply. Add a function which does the reverse - it will be needed in
later patches.

While at it, pull the other equiv table function up in the file so that
it can be used by other functionality without forward declarations.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Link: http://lkml.kernel.org/r/1344361461-10076-11-git-send-email-bp@amd64.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>