msm: mdss: Prevent AD on WFD configuration

Assertive display is not allowed on HDMI and WFD configurations.
However, since WFD uses the writeback path, and AD uses the
writeback path for earlier hardware, then we must check which
hardware configuration is being used when checking writeback
panel configuration to prevent or allow AD.

Change-Id: I85f7380d0345cad7785ed41e22df559bc5c1618e
Signed-off-by: Benet Clark <benetc@codeaurora.org>