mmc: sdhi: support up to 3 interrupt sources

Convert the SDHI code to support more than a single interrupt source.
Needed to support hardware that uses GIC instead of INTC as interrupt
controller.

Will also allow us to remove the irq forwarding workaround from the
INTC code in the future.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>