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/CPCI2DP_defconfig b/configs/CPCI2DP_defconfig
index 99e4ad0..470e070 100644
--- a/configs/CPCI2DP_defconfig
+++ b/configs/CPCI2DP_defconfig
@@ -2,6 +2,7 @@
 CONFIG_4xx=y
 CONFIG_TARGET_CPCI2DP=y
 CONFIG_BOOTDELAY=3
+CONFIG_VERSION_VARIABLE=y
 CONFIG_LOOPW=y
 CONFIG_CMD_I2C=y
 # CONFIG_CMD_SETEXPR is not set