phy: qcom-usb-hs: Add qcom,enable-vbus-pullup support

Downstream has a flag called qcom,dp-manual-pullup which informs the
downstream driver if it should toggle ULPI_MISC_A_VBUSVLDEXTSEL and
ULPI_MISC_A_VBUSVLDEXT.

Downstream states:

"qcom,dp-manual-pullup: If present, vbus is not routed to USB
        controller/phy and controller driver therefore enables pull-up
        explicitly before starting controller using usbcmd run/stop bit."

Working with a type-c controller which handles VBUS entirely means there's
a need to replicate similar logic in upstream.

The current PHY code waggles these bits if an extcon associated with VBUS
exists but, that is not the case when using a full-fat type-c controller
i.e. there's no VBUS line routed to a SoC pad to sense.

This patch enables and disables the VBUS pullup bits on PHY power_on and
power_off respectively if the DT has declared the bool
"qcom,enable-vbus-pullup".

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>