ARM: dts: msm: Add VBUS valid override to msm8974pro-ac and apq8084

Add flags indicating VBUS is not routed to the USB PHY on
MSM8974Pro-AC and APQ8084. This allows the driver to manually
enable/disable the D+ pull-up upon receiving external VBUS
notification from PMIC.

Change-Id: I444379a84a2a8d170d082c9c8c81395877f66d5a
Signed-off-by: Jack Pham <jackp@codeaurora.org>