configs: am43xx_evm: Enable NAND

AM43xx EVMs have NAND so enable it.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

configs/am43xx_evm_defconfig

 CONFIG_ARM=y
 CONFIG_TARGET_AM43XX_EVM=y
 CONFIG_SPL=y
-CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1"
+CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1,NAND"
 CONFIG_CMD_NET=y