soc: ti: omap-prm: Add basic power domain support

The PRM controller has currently only support for resets while the power
domains are still handled in the platform code.

Let's add basic power domain support to enable and disable a PRM
controlled power domain if configured in the devicetree. This can be
used for various hardware accelerators, and interconnect instances.

Further support can be added later on as needed for runtime configuration
based on domain-idle-states.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>