mmc: sdio_irq: rework sdio irq handling

Rather than the SDIO support spawning it's own thread for handling card
interrupts, use the generic IRQ infrastructure for this, triggering it
from the host interface's interrupt handling directly.

This avoids a race between the parent thread waiting to receive an
interrupt response from the card, and the slow startup from the sdio
irq thread, which can occur as a result of high system load (eg, while
udev is running.)

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Markus Pargmann <mpa@pengutronix.de>
Tested-by: Stephen Warren <swarren@nvidia.com>
[Ulf Hansson] Resolved conflict
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>