24xx PM: convert pm24xx.c code to use pwrdm/clkdm interfaces

24xx PM: convert pm24xx.c code to use pwrdm/clkdm interfaces

Convert the existing OMAP24xx pm24xx.c code to use the recent
powerdomain/clockdomain interface code.  This mostly consists of removing
direct register reads and writes and replacing it with code that can be
more generic.

Also update some of the comments to better reflect what is actually
happening on the chip.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>