edac: lock module owner to avoid error report conflicts

APEI GHES and i7core_edac/sb_edac currently can be loaded at
the same time, but those are Highlander modules:
	"There can be only one".

There are two reasons for that:

1) Each driver assumes that it is the only one registering at
   the EDAC core, as it is driver's responsibility to number
   the memory controllers, and all of them start from 0;

2) If BIOS is handling the memory errors, the OS can't also be
   doing it, as one will mangle with the other.

So, we need to add an module owner's lock at the EDAC core,
in order to avoid having two different modules handling memory
errors at the same time. The best way for doing this lock seems
to use the driver's name, as this is unique, and won't require
changes on every driver.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>