ARM: OMAP4: PM: Add MPUSS power domain OSWR support

This patch adds the MPUSS OSWR (Open Switch Retention) support. The MPUSS
OSWR configuration is as below.
	- CPUx L1 and logic lost, MPUSS logic lost, L2 memory is retained

OMAP4460 onwards, MPUSS power domain doesn't support OFF state any more
anymore just like CORE power domain. The deepest state supported is OSWR.
On OMAP4430 secure devices too, MPUSS off mode can't be used because of
a bug which alters Ducati and Tesla states. Hence MPUSS off mode as an
independent state isn't supported on OMAP44XX devices.

Ofcourse when MPUSS power domain transitions to OSWR along
with device off mode, it eventually hits off state since memory
contents are lost.

Hence the MPUSS off mode independent state is not attempted without
device off mode. All the necessary infrastructure code for MPUSS
off mode is in place as part of this series.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Jean Pihet <j-pihet@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Tested-by: Vishwanath BS <vishwanath.bs@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>