defconfigs: Migrate CONFIG_SYS_REDUNDAND_ENVIRONMENT

Move this symbol to Kconfig.  As part of this we can drop a UBI-specific
symbol that was a stop-gap for not having this particular symbol in
Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/mx31pdk_defconfig b/configs/mx31pdk_defconfig
index bdeb6b2..cdf0853 100644
--- a/configs/mx31pdk_defconfig
+++ b/configs/mx31pdk_defconfig
@@ -22,6 +22,7 @@
 CONFIG_CMD_PING=y
 CONFIG_CMD_DATE=y
 CONFIG_ENV_IS_IN_NAND=y
+CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_MXC_GPIO=y
 # CONFIG_MMC is not set
 CONFIG_NAND=y