msm: mdss: hdmi: check for scrambler override

In some cases, scrambling may need to be forced on or off based on
sink requirements. To support such requirements, scrambler override
may be imposed. If scrambler override has been enabled, use
override value to enable or disable scrambler.

Change-Id: I9556c6457258598e6b6758573bb0263d53e612da
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>