ARM: OMAP4+: PRM: register interrupt information from DT

Allow the PRM interrupt information to be picked up from device tree.
the only exception is for OMAP4 which uses values pre-populated and allows
compatibility with older dtb.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>