msm: mdss: add control to mdp core clock in HDMI driver

Any register access within MDP domain requires mdss ahb and mdp core
clocks to be enabled. In the use-case where HDMI is the only sub-module
enabled and its interrupt is triggered, lack of mdp core clock leads to
un-clocked access to MDSS interrupt register. Which in turn leads to
ahb bus timeout and device crash or reboot. Fix this by controlling mdp
core clock from HDMI driver.

Change-Id: I8479cf0905b41d085b912ddb6c4a9d83bc430ee8
CRs-Fixed: 482432
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>