ARM: OMAP2+: PRCM: split and relocate the PRM/CM globals setup

Split omap2_set_globals_prcm() into PRM, CM, and PRCM_MPU variants, since
these are all separate IP blocks.  This should make it easier to move the
PRM, CM, PRCM_MPU code into drivers/ in future patchsets.

At this point arch/arm/plat-omap/include/plat/prcm.h is empty; a
subsequent patch will remove it, and remove the #include from all the
files that #include it.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Tested-by: Vaibhav Hiremath <hvaibhav@ti.com>