EDAC/mce_amd: Make fam_ops static global

... and do not kmalloc a three-pointer struct. Which simplifies
mce_amd_init() a bit.

No functional changes.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200116163403.GF27148@zn.tnic