ibmpex: update Kconfig to list more supported models

Enhanced the list of supported machines.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Cc: Mark M. Hoffman <mhoffman@lightlink.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>