Convert CONFIG_TEGRA_GPU to Kconfig

This converts the following to Kconfig:
   CONFIG_TEGRA_GPU

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/mach-tegra/Kconfig b/arch/arm/mach-tegra/Kconfig
index 5309be9..09ad2d6 100644
--- a/arch/arm/mach-tegra/Kconfig
+++ b/arch/arm/mach-tegra/Kconfig
@@ -178,6 +178,10 @@
 source "arch/arm/mach-tegra/tegra210/Kconfig"
 source "arch/arm/mach-tegra/tegra186/Kconfig"
 
+config TEGRA_GPU
+	bool "Enable setting up the GPU"
+	depends on TEGRA124 || TEGRA210
+
 config CMD_ENTERRCM
 	bool "Enable 'enterrcm' command"
 	default y