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/cpu/armv7/omap4/Kconfig b/arch/arm/cpu/armv7/omap4/Kconfig
index 92eb2f4..48ce9d3 100644
--- a/arch/arm/cpu/armv7/omap4/Kconfig
+++ b/arch/arm/cpu/armv7/omap4/Kconfig
@@ -6,6 +6,9 @@
 config SPL_FAT_SUPPORT
 	default y
 
+config SPL_GPIO_SUPPORT
+	default y
+
 choice
 	prompt "OMAP4 board select"
 	optional