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/ma5d4evk_defconfig b/configs/ma5d4evk_defconfig
index 090f7fd..e3431ae 100644
--- a/configs/ma5d4evk_defconfig
+++ b/configs/ma5d4evk_defconfig
@@ -5,6 +5,7 @@
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="SAMA5D4"
 CONFIG_BOOTDELAY=3
+CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set