msm: mdss: force client clocks to be on while halting vbif

In order to successfully halt vbif client, need to ensure that client
core clock is on while halting and waiting acknowledge of vbif halt.

Change-Id: I9f17e90f34cf4b3033bc4f3b23e2c1df8fc3aa69
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>