ARM: OMAP2+: powerdomain: Wait for powerdomain transition in pwrdm_state_switch()

Commit b1cbdb00 ("OMAP: clockdomain: Wait for powerdomain to be ON
when using clockdomain force wakeup") was assuming that
pwrdm_state_switch() does wait for the powerdomain transition which is
not the case.  The missing wait for the powerdomain transition
violates the sequence which the hardware expects, which causes power
management failures on some devices.

Fix this API by adding the pwrdm_wait_transition().

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Rajendra Nayak <rnayak@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
[paul@pwsan.com: added some more details in the commit log]
Signed-off-by: Paul Walmsley <paul@pwsan.com>