ARM: OMAP4+: PM: Consolidate MPU subsystem PM code for re-use

OMAP5 and future OMAP based SOCs has backward compatible MPUSS
IP block with OMAP4. It's programming model is mostly similar.
Hence consolidate the OMAP MPUSS code so that it can be re-used
on OMAP5 and future SOCs.

No functional change.

Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>