common, kconfig: move VERSION_VARIABLE to Kconfig

move VERSION_VARIABLE from board config file into a
Kconfig option.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/configs/sh7757lcr_defconfig b/configs/sh7757lcr_defconfig
index b0d3f28..a80c10c 100644
--- a/configs/sh7757lcr_defconfig
+++ b/configs/sh7757lcr_defconfig
@@ -2,6 +2,7 @@
 CONFIG_SH_32BIT=y
 CONFIG_TARGET_SH7757LCR=y
 CONFIG_BOOTDELAY=3
+CONFIG_VERSION_VARIABLE=y
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_CONSOLE is not set
 # CONFIG_CMD_BOOTD is not set