x86/microcode/AMD: Simplify patch family detection

Instead of traversing the equivalence table, compute the family a patch
is for, from the processor revision ID in the microcode header.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: x86@kernel.org
Link: https://lkml.kernel.org/r/20181107170218.7596-8-bp@alien8.de