usb: phy: msm: Disable LDOs when suspending with cable disconnected

When the phy does not handle the vbus and id changes by itself
acting as a device and going into suspend with the cable disconnected,
turning off the phy's LDOs can also be performed to conserve more
power. This is already done by the HS phy.
To support this additional device tree property 'qcom,ext-vbus-id' was
added to the ss-phy node to indicate the phy does not handle vbus
and id changes.

Change-Id: Ia79459f95359a6c1b9de32ab9735640d6510cc0d
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>