usb: gadget: storage: fix mass storage gadgets to work with Synopsys UDC

The Synopsys USB device controller requires all OUT transfer request
lengths to be aligned to max packet size. The mass storage gadgets do
not meet this requirement for Super Speed. The gadgets already have a
function which performs this alignment for CBW packets, so use it for
data packets too.

The alternative would be to implement bounce buffers in the DWC3
driver, but that could have a significant impact on performance.

This version is based upon a more-correct patch written by Alan
Stern.

Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>