msm: mdss: hdcp_1x: enable HDP irq only for DP client

 HDCP driver provides a common interface for both Display port
 and HDMI clients. As HPD IRQ enable  API is valid only display
 Port, make sure it is handled gracefully when called
 from HDMI client so that invalid resource access can be avoided.

Change-Id: I42e07c6019300b37ea3426347fef571bbb6e278c
Signed-off-by: Vishnuvardhan Prodduturi <vproddut@codeaurora.org>