msm: qpnp-usbdetect: Add USB VBUS detection driver

This driver is used to enable detection of USB cable connection
based on VBUS voltage. The circuitry connects its detection
output to a PMIC GPIO which in turn will notify USB through
the power_supply_set_present() call.

This will be used on platforms in which VBUS is not directly
connected to the USB PHY and also in lieu of separate USB
charging circuitry that can do additionally do detection.

Change-Id: I6dd9e1a9740fc5af02b82a223eaeef2fafbf1057
Signed-off-by: Jack Pham <jackp@codeaurora.org>