disp: msm: sde: add support for AVR_STEP feature

Add AVR step support so SW can trigger a late frame and instead
of immediately triggering, HW will perform the update at the
start of the next step interval. This allows for a fixed SW
vsync timeline to be maintained in userland, eliminating the
usual drift from the actual HW vsync caused by a late frame.

This change adds AVR_STEP support via a DRM property.

Change-Id: I4cf8a296989805f134c2165a3bed0b050bb09c96
Signed-off-by: Steve Cohen <cohens@codeaurora.org>

msm/sde/sde_hw_intf.h

@@ -63,7 +63,8 @@ struct intf_tear_status {
 struct intf_avr_params {
 	u32 default_fps;
 	u32 min_fps;
-	u32 avr_mode; /* 0 - disable, 1 - continuous, 2 - one-shot */
+	u32 avr_mode; /* one of enum @sde_rm_qsync_modes */
+	u32 avr_step_lines; /* 0 or 1 means disabled */
 };
 
 /**