phy: ti-pipe3: Add SATA compatible to Documentation binding

SATA PHY needs a new compatible ID. Add it to the DT binding documentation.

Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>