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/omap3_beagle_defconfig b/configs/omap3_beagle_defconfig
index 19b697e..5fd86af 100644
--- a/configs/omap3_beagle_defconfig
+++ b/configs/omap3_beagle_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_OMAP3_BEAGLE=y
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="NAND"
+CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set