mfd: Add tps65910-irq devicetree init and irqdomain support

This change changes the tps65910-irq code to use irqdomain, and support
initialization from devicetree. This assumes that the irq_base in the
platform data is -1 if devicetree is used.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>