usb: gadget: Add qti_usb gadget driver

This change adds qti_gadget driver for early USB enumeration.
This is a snapshot of the driver from msm-4.14 as of commit
26acafd0651("usb: gadget: qti: Add support for MBIM OS descriptor
handling").

Change-Id: Ie6d3a6584d396132827949a30608d1efb2408e77
Signed-off-by: Elson Roy Serrao <eserrao@codeaurora.org>