drm/msm/dsi-staging: fix clk voting in cmd mode to support idle_pc

Enable/disable the DSI clks when required for cmd mode panels
rather than handling in suspend/resume. This would enable the
clks voting to go down and enter idle power collapse when the
dsi driver is in idle state. Remove clk voting from phy enable/
disable as it causes deadlock dsi driver comes out of idle state.

Change-Id: I5db4b04ac6d7ce7448b22e2d0e1ec5e3d6599f31
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>