sunxi: add gpio driver

sunxi: add gpio driver

This patch enables CONFIG_CMD_GPIO for the Allwinner (sunxi) platform as well
as providing the common gpio API (gpio_request/free, direction in/out, get/set
etc).

Signed-off-by: Chen-Yu Tsai <[email protected]>
Signed-off-by: Hans de Goede <[email protected]>
Signed-off-by: Ma Haijun <[email protected]>
Signed-off-by: Oliver Schinagl <[email protected]>
Signed-off-by: Ian Campbell <[email protected]>
Cc: Henrik Nordström <[email protected]>
Cc: Tom Cubie <[email protected]>
Acked-by: Hans de Goede <[email protected]>