pinctrl: sunxi: remove GPIO_EXTRA_HEADER

U-Boot's generic GPIO_EXTRA_HEADER is a convenience symbol to allow code
to more easily include platform specific GPIO headers. This should not
be needed in a DM world anymore, since the generic GPIO framework
handles that nicely.
For Allwinner boards we still need to deal with non-DM GPIO in the SPL,
but this should become the exception, not the rule.

Make this more obvious by removing the definition of GPIO_EXTRA_HEADER,
and just force every legacy user of platform specific GPIO to include
the new sunxi_gpio.h header explicitly. Everyone doing so should feel
ashamed and should find a way to avoid it from now on.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Samuel Holland <samuel@sholland.org>
diff --git a/drivers/pinctrl/sunxi/pinctrl-sunxi.c b/drivers/pinctrl/sunxi/pinctrl-sunxi.c
index 946447e..fc80fe5 100644
--- a/drivers/pinctrl/sunxi/pinctrl-sunxi.c
+++ b/drivers/pinctrl/sunxi/pinctrl-sunxi.c
@@ -7,6 +7,7 @@
 #include <dm/pinctrl.h>
 #include <errno.h>
 #include <malloc.h>
+#include <sunxi_gpio.h>
 
 #include <asm/gpio.h>