Convert the OMAP clock code's _omap2_module_wait_ready() to use
SoC-independent CM functions that are provided by the CM code, rather
than using a deprecated function from mach-omap2/prcm.c.

This facilitates the future conversion of the CM code to a driver, and
also removes a mach-omap2/prcm.c user.  mach-omap2/prcm.c will be removed
by a subsequent patch.

Some modules have IDLEST registers that aren't in the CM module, such
as the AM3517 IDLEST bits.  So we also need a fallback function for
these non-CM odd cases.  Create a temporary one in mach-omap2/clock.c,
intended to exist until the SCM drivers are ready.
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Tested-by: Vaibhav Hiremath <hvaibhav@ti.com>