phy: ti: phy-da8xx-usb: Add runtime PM support

phy: ti: phy-da8xx-usb: Add runtime PM support

Runtime PM is not supported while USB PHY can be turned off from
register accesses.

Add runtime PM for the USB2.0 PHY. The PHY is entirely shut down to save
as much power as possible. This means that gadgets will not be discovered
once suspend state is entered, and suspend state can not be left without
an explicit user intervention (through sysfs). That's why runtime PM is
disabled by default.

Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com>
Link: https://lore.kernel.org/r/20240528102026.40136-2-bastien.curutchet@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>