disp: msm: sde: fix TUI CRTC selection for dual-display

Currently, driver is always querying CRTC-0 to determine if
a TUI session is active or not independently of where the request
is coming from (PVM/TVM) and the display it is intended to. This
leads to an invalid CRTC selection in dual-display use case as
the CRTC must be dynamically selected depending on the display
selection.

This change adds helper functions to dynamically query the
CRTC with an active VM request and uses those helpers in
PVM ops.

Change-Id: I62ef46a1f23bb812287ab1545e444b90eb8f554c
Signed-off-by: Amine Najahi <anajahi@codeaurora.org>