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/brppt1_spi_defconfig b/configs/brppt1_spi_defconfig
index fee9973..fc1f1e6 100644
--- a/configs/brppt1_spi_defconfig
+++ b/configs/brppt1_spi_defconfig
@@ -5,6 +5,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1,SPI_BOOT,EMMC_BOOT"
 CONFIG_SPI_BOOT=y
 CONFIG_BOOTDELAY=-2
+CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set