sh: sh4: Add CONFIG_SH4 definition to config.mk of SH4

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/arch/sh/cpu/sh4/config.mk b/arch/sh/cpu/sh4/config.mk
index c357557..753580b 100644
--- a/arch/sh/cpu/sh4/config.mk
+++ b/arch/sh/cpu/sh4/config.mk
@@ -8,5 +8,5 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 #
-PLATFORM_CPPFLAGS += -m4-nofpu
+PLATFORM_CPPFLAGS += -DCONFIG_SH4 -m4-nofpu
 PLATFORM_RELFLAGS += -ffixed-r13