[PATCH] edac: mark as experimental

EDAC is still causing a few problems and the code is relatively green.  Mark
it as experimental until thing settle down.

Also, provide some documentation pointers in Kconfig help.

Signed-off-by: Tim Small <tim@buttersideup.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>