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/kmtegr1_defconfig b/configs/kmtegr1_defconfig
index b450499..f0b1cca 100644
--- a/configs/kmtegr1_defconfig
+++ b/configs/kmtegr1_defconfig
@@ -4,6 +4,7 @@
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_STDOUT_VIA_ALIAS=y
 CONFIG_SYS_EXTRA_OPTIONS="KMTEGR1"
+CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Hit <SPACE> key to stop autoboot in %2ds\n"