sh: consolidate CONFIG_SYS_CPU defines

Now each board selects one of CONFIG_CPU_SH2, CONFIG_CPU_SH3,
CONFIG_CPU_SH4, so let's move CONFIG_SYS_CPU definition to
arch/sh/Kconfig.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 49b00da..a77e6f9 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -1,9 +1,6 @@
 menu "SuperH architecture"
 	depends on SH
 
-config SYS_ARCH
-	default "sh"
-
 config CPU_SH2
 	bool
 
@@ -110,6 +107,14 @@
 
 endchoice
 
+config SYS_ARCH
+	default "sh"
+
+config SYS_CPU
+	default "sh2" if CPU_SH2
+	default "sh3" if CPU_SH3
+	default "sh4" if CPU_SH4
+
 source "board/alphaproject/ap_sh4a_4a/Kconfig"
 source "board/espt/Kconfig"
 source "board/mpr2/Kconfig"