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-tegra/Kconfig b/arch/arm/mach-tegra/Kconfig
index 1eaf406..6b1cedf 100644
--- a/arch/arm/mach-tegra/Kconfig
+++ b/arch/arm/mach-tegra/Kconfig
@@ -1,5 +1,8 @@
 if TEGRA
 
+config SPL_GPIO_SUPPORT
+	default y
+
 config TEGRA_IVC
 	bool "Tegra IVC protocol"
 	help