nxp-s32g: usb: chipedea: add ulpi usb phy support

Add initialization for the structure usb_phy.

And a series of operations "flush-stop-reset" is needed so that we can
access usb phy via ULPI interface.

And otg_set_vbus is called after the host mode is determined because
we need call ulpi_set_vbus to set vbus via it.

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>