MMC: OMAP: Start new commands from work queue instead of irq

Use work queues for starting new commands instead of starting them
directly from irq handler. The command scheduling needs to be delayed
a bit for some cards which should not be done from an interrupt.

Signed-off-by: Jarkko Lavinen <jarkko.lavinen@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>