msm: mdss: request bus bandwidth before panel on

Panel on sequence requires access to bus, make sure bus clock is enabled
before panel on by requesting bandwidth for panel commands.

Change-Id: I2f92e81b20dba7875a8b1160d14e8fa1895c8f15
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>