mfd: Drop twl4030-irq's edge_work

... and do all the synchronization with the
hardware during bus_sync_unlock. We can now
remove all the workqueues.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>