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/at91sam9260ek_nandflash_defconfig b/configs/at91sam9260ek_nandflash_defconfig
index 3b4706b..2a2c9a6 100644
--- a/configs/at91sam9260ek_nandflash_defconfig
+++ b/configs/at91sam9260ek_nandflash_defconfig
@@ -29,6 +29,7 @@
 CONFIG_OF_CONTROL=y
 CONFIG_DEFAULT_DEVICE_TREE="at91sam9260ek"
 CONFIG_ENV_IS_IN_NAND=y
+CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_DM=y
 CONFIG_CLK=y
 CONFIG_CLK_AT91=y