disp: add binding documentation for sde-intf-tear-irq-off

Add documentation for the new SDE device tree node which gives
the INTF TE IRQ offsets. This is required for TE support on
all targets with refactored interrupt support (kernel 5.4+).

Change-Id: I8bae73b1407e39c9dcf2ee95a2e0d7aed1e50fd2
Signed-off-by: Steve Cohen <cohens@qti.qualcomm.com>