s3cmci: make SDIO IRQ hardware IRQ support build-time configurable

We have found a couple of boards where the SDIO IRQ hardware support has
failed to work properly, and thus we should make it configurable whether
or not to be included in the driver.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>