clk: qcom: mdss: update resource management in PLL driver

Remove mutex and ref count variables that synchronize the
resource enable and disable calls since the regulator
and clock drivers take care of maintaining the ref
count for each resource. Also, remove resource enable
and disable calls from mux_set_rate/mux_get_rate/clk_enable
context of the DSI branch clocks to avoid warnings.

Change-Id: Ieb32141156afcce008b3555af476c20f888f064b
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>