drm/msm/dp: add support to force HDCP 2.2 encryption

The HDCP 2.2 TrustZone application on sm8150 will only enable
encryption based on the content being played back. Add debug
support to force HDCP 2.2 encryption for DisplayPort in order
to pass compliance testing.

CRs-Fixed: 2284465
Change-Id: I84e29000f49237babd5804982986b02063f30673
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>