usb: gadget: Reset string ids upon unbind

String ids for qdss,cdev and gsi based interfaces
are re-used even though the device re-enumerates.
This is causing string id sequence mismatch and resulting
in adb using the string id of qdss interface. Reset the
string ids for these functions in their respective unbind
calls to fix this issue.

Change-Id: Ia9b196734a99ccc2e8c35073ec4e535755774c16
Signed-off-by: Elson Roy Serrao <eserrao@codeaurora.org>