sunxi: axp: Add driver-model support to the axp_gpio code

Add driver-model support to the axp_gpio code, note that this needs a small
tweak to the driver-model version of sunxi_name_to_gpio to deal with the
vbus detect and enable pins which are not standard numbered gpios.

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