arc: arcangel4: set board entry <none> to fix a build error

There are no source files in board/synopsys/arcangel4/
directory.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Alexey Brodkin <Alexey.Brodkin@synopsys.com>

board/synopsys/arcangel4/Makefile

@@ -1,11 +0,0 @@
-#
-# Copyright (C) 2013-2014 Synopsys, Inc. All rights reserved.
-#
-# SPDX-License-Identifier:	GPL-2.0+
-#
-
-# This board is mostly used for debugging U-Boot in simulation (ISS).
-# The only peripheral which is used on this board is a serial port which
-# requires no initialization except those in "include/configs/arcangel4.h".
-# And now there's no specific initializations for this board.
-# So this Makefile is only required for satisfaction of U-Boot build system.

boards.cfg

@@ -44,9 +44,9 @@
 ###########################################################################################################
 
 Active  aarch64     armv8          -           armltd          vexpress64          vexpress_aemv8a                      vexpress_aemv8a:ARM64                                                                                                             David Feng <fenghua@phytium.com.cn>
-Active  arc         arc700         -           synopsys        -                   arcangel4                            -                                                                                                                                 Alexey Brodkin <abrodkin@synopsys.com>
+Active  arc         arc700         -           synopsys        <none>              arcangel4                            -                                                                                                                                 Alexey Brodkin <abrodkin@synopsys.com>
 Active  arc         arc700         -           synopsys        -                   axs101                               -                                                                                                                                 Alexey Brodkin <abrodkin@synopsys.com>
-Active  arc         arc700         -           synopsys        arcangel4           arcangel4-be                         -                                                                                                                                 Alexey Brodkin <abrodkin@synopsys.com>
+Active  arc         arc700         -           synopsys        <none>              arcangel4-be                         -                                                                                                                                 Alexey Brodkin <abrodkin@synopsys.com>
 Active  arm         arm1136        -           armltd          integrator          integratorcp_cm1136                  integratorcp:CM1136                                                                                                               Linus Walleij <linus.walleij@linaro.org>
 Active  arm         arm1136        mx31        -               -                   imx31_phycore                        -                                                                                                                                 -
 Active  arm         arm1136        mx31        davedenx        -                   qong                                 -                                                                                                                                 Wolfgang Denk <wd@denx.de>