msm: mdss: hdmi: handle CEC interrupts if CEC feature is enabled

Handle CEC interrupts in the CEC hardware module only if the CEC
feature is explicitly enabled by the CEC framework. This will
prevent the CEC hardware module from unnecessarily processing
interrupts that will not be handled by the CEC framework (if
the feature is not explicity enabled).

CRs-Fixed: 1016853
Change-Id: I5110f2c8277581f87da71f962560c33f65582176
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>