msm: mdss: decouple clk ctrl and bw ctrl

Move bandwidth control to panel on and off functions
to speed up the clock control.

CRs-Fixed: 673613
Change-Id: Ib3828687ab54fb7a5aad7e97dec46c6e76a7311a
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>