rename symbol: CONFIG_TEGRA -> CONFIG_ARCH_TEGRA

Have this symbol follow the pattern of all other such symbols.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
diff --git a/disk/Kconfig b/disk/Kconfig
index 747275c..cee16a8 100644
--- a/disk/Kconfig
+++ b/disk/Kconfig
@@ -53,7 +53,7 @@
 	bool "Enable ISO partition table"
 	depends on PARTITIONS
 	default y if DISTRO_DEFAULTS
-	default y if MIPS || TEGRA
+	default y if MIPS || ARCH_TEGRA
 
 config SPL_ISO_PARTITION
 	bool "Enable ISO partition table for SPL"
@@ -75,7 +75,7 @@
 	bool "Enable EFI GPT partition table"
 	depends on PARTITIONS
 	default y if DISTRO_DEFAULTS
-	default y if TEGRA
+	default y if ARCH_TEGRA
 	select LIB_UUID
 	help
 	  Say Y here if you would like to use device under U-Boot which