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/sequoia_ramboot_defconfig b/configs/sequoia_ramboot_defconfig
index 3fd8b25..65ae39a 100644
--- a/configs/sequoia_ramboot_defconfig
+++ b/configs/sequoia_ramboot_defconfig
@@ -4,6 +4,7 @@
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_SYS_EXTRA_OPTIONS="SEQUOIA,SYS_RAMBOOT,SYS_TEXT_BASE=0x01000000,SYS_LDSCRIPT=board/amcc/sequoia/u-boot-ram.lds"
 CONFIG_BOOTDELAY=5
+CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y