Convert CONFIG_SPL_GPIO_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-exynos/Kconfig b/arch/arm/mach-exynos/Kconfig
index c25fcf3..d4a5bc9 100644
--- a/arch/arm/mach-exynos/Kconfig
+++ b/arch/arm/mach-exynos/Kconfig
@@ -61,6 +61,9 @@
 
 if ARCH_EXYNOS5
 
+config SPL_GPIO_SUPPORT
+	default y
+
 choice
 	prompt "EXYNOS5 board select"