usb: gadget: Support already-mapped DMA SGs

Add a new 'sg_was_mapped' field to the struct usb_request. This field
can be used to indicate that the scatterlist associated to the USB
transfer has already been mapped into the DMA space, and it does not
have to be done internally.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20240130122340.54813-2-paul@crapouillou.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>