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

Add lineptr interrupt support by making use of INTR_PROG_LINE
register part of the interfaces. This would generate the interrupt
when the configured pixel location in the panel video timing in terms
of video raster structure is reached for the frame. The lineptr can
be updated through the lineptr_value node. Any modification to the value
would take effect immediately for video mode panels.

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: I33c09b2dcfc7b49ce94f5e31b5b297b0445fd073
Acked-by: Mike Mager <mikemager@codeaurora.org>
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>