USB: musb: disable double buffering for older RTL versions

Trying to use double buffer modes in RTL versions <2.0 may result in
infinite hangs or data corruption.  So avoid them with older versions.

Signed-off-by: Cliff Cai <cliff.cai@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>