Documentation: dt: reset: Add TI SCI reset binding

Add TI SCI reset controller binding. This describes the DT binding
details for a reset controller node providing reset management services
to hardware blocks (reset consumers) using the Texas Instrument's System
Control Interface (TI SCI) protocol to communicate to a system controller
block present on the SoC.

Signed-off-by: Andrew F. Davis <afd@ti.com>
[s-anna@ti.com: revise the binding format]
Signed-off-by: Suman Anna <s-anna@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>