sunxi: gpio: Build sunxi_name_to_gpio_bank for driver-model code too

When doing a driver-model enabled build we still need sunxi_name_to_gpio_bank
(for now) for the mmc pinmux code in board/sunxi/board.c, so build it for
driver-model enabled builds too.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Ian Campbell <ijc@hellion.org.uk>