ARM: OMAP2xxx: APLL/CM: convert to use omap2_cm_wait_module_ready()

Convert the OMAP2xxx APLL code to use omap2_cm_wait_module_ready(),
and move the low-level CM register manipulation functions to
mach-omap2/cm2xxx.c.  The objectives here are to remove the dependency
on the deprecated omap2_cm_wait_idlest() function in
mach-omap2/prcm.c, so that code can be removed later; and move
low-level register accesses to the CM IP block to the CM code, which
will soon be moved into drivers/.

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