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/am43xx_evm_ethboot_defconfig b/configs/am43xx_evm_ethboot_defconfig
index a980c99..8676f32 100644
--- a/configs/am43xx_evm_ethboot_defconfig
+++ b/configs/am43xx_evm_ethboot_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_AM43XX_EVM=y
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1,NAND,SPL_ETH_SUPPORT"
+CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set