sh: Move SH_32BIT to Kconfig

This moves SH_32BIT to Kconfig, and removes SH_32BIT from config
files.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/configs/sh7753evb_defconfig b/configs/sh7753evb_defconfig
index 9ff4121..35809e9 100644
--- a/configs/sh7753evb_defconfig
+++ b/configs/sh7753evb_defconfig
@@ -1,2 +1,3 @@
 CONFIG_SH=y
+CONFIG_SH_32BIT=y
 CONFIG_TARGET_SH7753EVB=y