sunxi: gpio: Remove name_to_gpio macro

sunxi: gpio: Remove name_to_gpio macro

This clarifies which callers must be updated to complete the DM_GPIO
conversion.

The only remaining caller of name_to_gpio in generic code is inside the
!DM_GPIO block in cmd/gpio.c. DM_GPIO is always selected on sunxi, so
that code cannot be reached. And after this commit, there are only two
remaining implementations of name_to_gpio.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>