EDAC/amd64: Set maximum channel layer size depending on family

The AMD64 EDAC module currently hardcodes the EDAC channel layer size
count to two. Future AMD systems may have more channels than this.

Set the EDAC channel layer size equal to the maximum number of channels
possible for the system. On Family 17h and later, this is set in the
num_umcs variable. Older systems will continue to use two as the
default.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: James Morse <james.morse@arm.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: https://lkml.kernel.org/r/20190325203319.7603-1-Yazen.Ghannam@amd.com