Implement VBUS session handling for FOTG210. This is
mainly used by the UDC driver which needs to call down to
the FOTG210 core and enable/disable VBUS, as this needs to be
handled outside of the HCD and UDC drivers, by platform
specific glue code.

The Gemini has a special bit in a system register to turn
VBUS on and off so we implement this in the FOTG210 core.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230103-gemini-fotg210-usb-v2-7-100388af9810@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>