OMAP2+: PM: idle clkdms only if already in idle

The omap_set_pwrdm_state function forces clockdomains
to idle, without checking the existing idle state
programmed, instead based solely on the HW capability
of the clockdomain to support idle.
This is wrong and the clockdomains should be idled
post a state_switch *only* if idle transitions on the
clockdomain were already enabled.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>