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/brxre1_defconfig b/configs/brxre1_defconfig
index 2567a40..3895eec 100644
--- a/configs/brxre1_defconfig
+++ b/configs/brxre1_defconfig
@@ -3,6 +3,7 @@
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1"
 CONFIG_BOOTDELAY=-2
+CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_BOOTD is not set
 # CONFIG_CMD_BOOTM is not set