ARM: OMAP4+: PM: use only valid low power state for suspend

We are using power domain state as RET and logic state as OFF. This
state is OSWR. This may not always be supported on ALL power domains. In
fact, on certain power domains, this might result in a hang on certain
platforms. Instead, depend on powerdomain data to provide accurate
information about the supported powerdomain states and use the
appropriate function to query and use it as part of suspend path.

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