add back the base-files/image code from brcm-2.4 to brcm47xx

SVN-Revision: 21945

target/linux/brcm47xx/base-files/lib/upgrade/platform.sh

@@ -0,0 +1,16 @@
+PART_NAME=linux
+
+platform_check_image() {
+	[ "$ARGC" -gt 1 ] && return 1
+
+	case "$(get_magic_word "$1")" in
+		# .trx files
+		4844) return 0;;
+		*)
+			echo "Invalid image type. Please use only .trx files"
+			return 1
+		;;
+	esac
+}
+
+# use default for platform_do_upgrade()