omap2+: mux: Remove the use of IDLE flag

Currently OMAP_DEVICE_PAD_IDLE flag is used to mux pins
dynamically. This can be simplified by using the enabled
state variable of each pad. This also fixes the issue of
the static pads not getting muxed after idling and
disable/enable state transitions.

Signed-off-by: sricharan <r.sricharan@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>