msm: mdss: hdmi: Use SCM calls for secure HDCP registers

Use TZ (Trust Zone) secure API to program HDCP (High-bandwidth
Digital Content Protection) registers to aviod unauthorized
access.

Change-Id: I7533babd1e626cd032dd4e3e8231f5ac3061ecec
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>