edac: make i82443bxgx_edac coexist with intel_agp

Fix 443BX/GX MCH suppport in a EDAC.

It makes i82443bxgx_edac coexist with intel_agp using the same approach as
several other EDAC drivers.

Tested on Intel's L443GX with redhat's 2.6.18 with whole EDAC subsystem
backported a while ago.

[root@host ~]# dmesg|grep -iE '(AGP|EDAC)'
Linux agpgart interface v0.101 (c) Dave Jones
agpgart: Detected an Intel 440GX Chipset.
agpgart: AGP aperture is 64M @ 0xf8000000
EDAC MC: Ver: 2.1.0 Jun 27 2008
EDAC MC0: Giving out device to 'i82443bxgx_edac' 'I82443BXGX': DEV 0000:00:00.0
EDAC PCI0: Giving out device to module 'i82443bxgx_edac' controller 'EDAC PCI controller': DEV '0000:00:00.0' (POLLED)

Signed-off-by: Vladislav Bogdanov <slava@nsys.by>
Cc: Doug Thompson <norsk5@yahoo.com>
Cc: Dave Airlie <airlied@linux.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>