Revert "usb:gadget Separated decoding functions from dwc3 driver."

This reverts commit 3db1b636.

It's broken.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Pawel Laszczak <pawell@cadence.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>