imx: mx6ull: fix USB bmode for i.MX 6UL and 6ULL

i.MX 6UL and 6ULL have different boot device capabilities and
use therefor use a different boot device selection table than
other i.MX 6 devices. Particularly, the value which has been
used so far (b0001) is assigned to QSPI boot for these two
devices.

There is no common reserved value for all i.MX 6devices. Use
b0010 for i.MX 6UL and 6ULL via compile time ifdef.

Reported-by: Joël Esponde <joel.esponde@honeywell.com>
Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Joël Esponde <joel.esponde@honeywell.com>