msm: mdss: hdcp1x: handle hpd for hdcp use-cases

On receiving attention command from displayport with hpd high,
proceed with hdcp authentication. Also, once the authentication
is successful, enable the encryption.

Change-Id: I970545bbf99ba89804016844f5b294a7e762e6e5
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>