ARM: OMAP AM33xx: PRM: add PRM support

As far as PRM/CM/PRCM modules are concerned, AM33XX device is
different than OMAP3 and OMAP4 architectures; so we need to handle it
separately.  This patch adds support for the PRM APIs required for
AM33XX device.

Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Afzal Mohammed <afzal@ti.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Rajendra Nayak <rnayak@ti.com>
[paul@pwsan.com: separated the PRM parts of "ARM: OMAP3+: am33xx: Add
 powerdomain & PRM support" into this patch; fixed Makefile prm33xx.o
 location; cleaned up some checkpatch violations; updated for 3.5]
Signed-off-by: Paul Walmsley <paul@pwsan.com>