phy-sun4i-usb: Add id and vbus detection support for the otg phy (phy0)

The usb0 phy is connected to an OTG controller, and as such needs some special
handling:

1) It allows explicit control over the pullups, enable these on phy_init and
disable them on phy_exit.

2) It has bits to signal id and vbus detect to the musb-core, add support for
for monitoring id and vbus detect gpio-s for use in dual role mode, and set
these bits to the correct values for operating in host only mode when no
gpios are specified in the devicetree.

While updating the devicetree binding documentation also add documentation
for the sofar undocumented usage of regulators for vbus for all 3 phys.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>