msm: mdss: add lineptr interrupt support for command mode panels

Add lineptr interrupt support by making use of the mdp write pointer
interrupt. This would make use of the hw feature to generate interrupts
when the display read pointer reaches the configured value. Expose event
and lineptr sysfs nodes to monitor and to configure the lineptr values.
The lineptr handlers are added during kickoff and removed during pingpong
work done. The configured lineptr value gets effect only in the next
kickoff. This feature is currently supported only for command mode panels.
It would skip setting the handlers for partial update frames, as the
feature is supported only with full frame updates.

Write a value from 1 to [line size] to enable interrupts, 0 to disable:
	/sys/devices/virtual/graphics/fb0/lineptr_value

To handle interrupt, read from:
	/sys/devices/virtual/graphics/fb0/lineptr_event

Change-Id: Id044d1bad4159955078ccab4d4dc82807d7e6102
Acked-by: Mike Mager <mikemager@qti.qualcomm.com>
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>