disp: msm: sde: fix panel mode check during SUI validations

During SUI validations and transitions, the encoders
are iterated to find the panel-mode. If concurrent
writeback is enabled, it is assumed as video mode.
Add check to consider only the built-in display
panel mode during sui to avoid wrong interpretation.

Change-Id: I2901eb29a0799571a95f6ab6f9f3f2c6154424c5
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>

msm/sde/sde_encoder.h

@@ -319,6 +319,14 @@ bool sde_encoder_in_clone_mode(struct drm_encoder *enc);
  */
 bool sde_encoder_is_primary_display(struct drm_encoder *enc);
 
+/**
+ * sde_encoder_is_dsi_display - checks if underlying display is DSI
+ *     display or not.
+ * @drm_enc:    Pointer to drm encoder structure
+ * @Return:     true if it is primary display. false if secondary display
+ */
+bool sde_encoder_is_dsi_display(struct drm_encoder *enc);
+
 /**
  * sde_encoder_control_idle_pc - control enable/disable of idle power collapse
  * @drm_enc:    Pointer to drm encoder structure