MIPS: kconfig: add options for vct board variant select

The vct board can be built with various variants which are
configured via CONFIG_SYS_EXTRA_OPTIONS. This is deprecated. Thus
add new Kconfig options for those board variants.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Acked-by: Stefan Roese <sr@denx.de>
diff --git a/configs/vct_premium_small_defconfig b/configs/vct_premium_small_defconfig
index 96bb0ee..1ce0efd 100644
--- a/configs/vct_premium_small_defconfig
+++ b/configs/vct_premium_small_defconfig
@@ -1,5 +1,6 @@
-CONFIG_SYS_EXTRA_OPTIONS="VCT_PREMIUM,VCT_SMALL_IMAGE"
 CONFIG_MIPS=y
 CONFIG_TARGET_VCT=y
 CONFIG_SYS_BIG_ENDIAN=y
+CONFIG_VCT_PREMIUM=y
+CONFIG_VCT_SMALL_IMAGE=y
 # CONFIG_CMD_CRC32 is not set