USB: gadget: use ep5 for bulk-in and ep6 for bulk-out for Blackfin MUSB

Normally, the musb uses ep1 as the bidirectional bulk endpoint.  This won't
work on the Blackfin musb as all endpoints (except ep0) are unidirectional.
Further, ep1-ep4 have a small 128 byte FIFO which makes them undesirable
for bulk endpoints (which need more like a 512 byte FIFO).  This leaves us
with ep5-ep7 which have 1024 byte FIFOs and can be configured as either
in/out and bulk/interrupt/iso on the fly.

Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Cliff Cai <cliff.cai@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>