phy: ti-pipe3: Add clocks to PIPE3 PHY Documentation binding

Add wakeup, system and reference clocks to 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>