sunxi: Add mmc0 card detect pin for Sinlinx SinA33

Sinlinx SinA33 uses PB4 for mmc0 card detect.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>