msm: rpm-regulator: Replace spinlocks with mutex locks

All calls of rpm_vreg_set_voltage() now take place in process
context.  Clock driver code on all targets has been written so
that atomic regulator control is no longer needed.

Refactor the rpm-regulator driver so that a mutex locks are used
in place of a spinlocks for sleep-selectable regulators which are
controlled via the rpm_vreg_set_voltage() function.

At the same time, move clk_prepare() and clk_unprepare calls in
the TCXO workaround so that these functions are correctly called
during each workaround invocation.  This is needed so that TCXO
isn't kept on forever after a single clk_prepare() call.

Change-Id: I07caed041dac6da073a0644271df2227b6c5a96e
Signed-off-by: David Collins <collinsd@codeaurora.org>