ARM: OMAP5 / DRA7: Enable CPU RET on suspend

On OMAP5 / DRA7, prevent a CPU powerdomain OFF and resulting MPU OSWR
and instead attempt a CPU RET and side effect, MPU RET in suspend.

NOTE: the hardware was originally designed to be capable of achieving
deep power states such as OFF and OSWR, however due to various issues
and risks, deepest valid state was determined to be CSWR - hence we use
the errata framework to handle this case.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
[nm@ti.com: updates]
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>