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/sh7785lcr_32bit_defconfig b/configs/sh7785lcr_32bit_defconfig
index 7cf93b4..31b84ff 100644
--- a/configs/sh7785lcr_32bit_defconfig
+++ b/configs/sh7785lcr_32bit_defconfig
@@ -1,3 +1,3 @@
-CONFIG_SYS_EXTRA_OPTIONS="SH_32BIT=1"
 CONFIG_SH=y
+CONFIG_SH_32BIT=y
 CONFIG_TARGET_SH7785LCR=y