x86: ucode-amd: Move family check to microcde_amd.c's init function

... to avoid useless trial to load firmware on systems with
unsupported AMD CPUs.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: Mike Travis <travis@sgi.com>
Cc: Tigran Aivazian <tigran@aivazian.fsnet.co.uk>
Cc: Borislav Petkov <borislav.petkov@amd.com>
Cc: Andreas Mohr <andi@lisas.de>
Cc: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20091117070638.GA27691@alberich.amd.com>
[ v2: changed BUG_ON() to WARN_ON() ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>