disp: msm: sde: bound crts and encoders for TUI displays

Currently, when starting a TUI session on a secondary display,
user-mode will select CRTC[1]/DSI-2 to initiate the session in
PVM and select CRTC[0]/DSI-2 in TVM to drive the frame. This
breaks existing cont. splash assumption that secondary display
will be using CRTC[1] in TVM session. Instead, driver can inform
user-mode of the possible CRTCs to use for each of the encoders.

This change sets the possible_crtcs variable on both DSI encoders
so that user-mode selects DSI-1/CRTC[0] and DSI-2/CRTC[1] in the
TVM use case.

Change-Id: Ic68f92901e42db80fb97799a05d11b5f3473af97
Signed-off-by: Amine Najahi <anajahi@codeaurora.org>