USB: isp1760: allow platform devices to customize devflags

Platform device support was merged earlier, but support for boards to
customize the devflags aspect of the controller was not.  We want this on
Blackfin systems to control the bus width, but might as well expose all of
the fields while we're at it.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>