soc: ti: pm33xx: Simplify RTC usage to prepare to drop platform data

We must re-enable the RTC module clock enabled in RTC+DDR suspend, and
pm33xx has been using platform data callbacks for that. Looks like for
retention suspend the RTC module clock must not be re-enabled.

To remove the legacy platform data callbacks, and eventually be able to
drop the RTC legacy platform data, let's manage the RTC module clock
and register range directly in pm33xx.

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