[SCSI] fix pcmcia compile problem

This patch

commit 8ae732a9
Author: Tejun Heo <htejun@gmail.com>
Date:   Fri Dec 7 22:36:23 2007 +0900

    [SCSI] make pcmcia directory use obj-y|m instead of subdir-y|m

Moved the scsi Makefile into conformance, but also caused the pcmcia
subdirectory to get built in for the first time, leading to duplicate
symbols in an allyesconfig build.  Since evidently no-one relies on
these being built in, fix this by ensuring they can only be built as
modules.

Acked-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>