dts: sdm845-db845c: add u-boot fixups

dts: sdm845-db845c: add u-boot fixups

The USB VBUS supply for the type-A port is enabled via a GPIO regulator.
This is incorrectly modelled in Linux where only the PCIe dependency is
expressed. The correct way to handle this will be through a
usb-connector node, but for now we'll just mark the regulator as
always-on so that it will be enabled automatically during boot.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>