msm: vidc: unprepare clocks during power collapse

If any clock is still prepared (only disabled), apps will
not vote for XO shutdown. Unprepared clocks will remove the
vote and facilitate XO shutdown.
During power collapse, video drivers now disable and
unprepare venus clocks.
There was minimal power savings during internal tests,
but customer reported to have impact of 13mA without
the change.
The change add different clock states. Clock state
transitions with clock api is shown below

====================  clk_prepare_enable()    ==================
|DISABLED_UNPREPARED| ----------------------  |ENABLED_PREPARED|
====================  clk_disable_unprepare() ==================
   ||                                                   ||
   || clk_unprepare() ================    clk_disable() ||
    -----------------|DISABLED_PREPARED| ---------------
      clk_prepare()   ================    clk_enable()

Change-Id: Id23302e359abcdf91c993835c6353fb251c96fe6
CRs-Fixed: 604629
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>