usb: dwc3: keystone: Turn on USB3 PHY before controller

The Local Power Sleep Controller (LPSC) dependency on AM65
requires SERDES0 to be powered on before USB.

We need to power up SERDES0 power domain and hold it on
throughout the reset, init, power on sequence.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>