s3cmci: add SDIO IRQ support

The controller supports SDIO IRQ detection so add support for hardware
assisted SDIO interrupt detection for the SDIO core.  This improves the
response time for SDIO interrupts and thus the transfer rate from devices
such as the Marvel 8686.

As a note, it does seem that the controller will miss an IRQ than is held
asserted, so there are some manual checks to see if the SDIO interrupt is
active after a transfer.

Major testing on the S3C2440.

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>