usb: chipidea: Add support for ULPI PHY bus

Some phys for the chipidea controller are controlled via the ULPI
viewport. Add support for the ULPI bus so that these sorts of
phys can be probed and read/written automatically without having
to duplicate the viewport logic in each phy driver.

Acked-by: Peter Chen <peter.chen@nxp.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>