configs: at91: Remove CONFIG_SYS_EXTRA_OPTIONS assignment

To remove the assignment of CONFIG_SYS_EXTRA_OPTIONS option,
which is deprecated, use the CONFIG_XXXX_BOOT options to
indicate the boot media, and the SoC is selected by the board.

Signed-off-by: Wenyou Yang <wenyou.yang@microchip.com>
diff --git a/configs/sama5d3_xplained_nandflash_defconfig b/configs/sama5d3_xplained_nandflash_defconfig
index 904c31b..65af64f 100644
--- a/configs/sama5d3_xplained_nandflash_defconfig
+++ b/configs/sama5d3_xplained_nandflash_defconfig
@@ -11,7 +11,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="at91-sama5d3_xplained"
 CONFIG_DEBUG_UART=y
 CONFIG_FIT=y
-CONFIG_SYS_EXTRA_OPTIONS="SAMA5D3,SYS_USE_NANDFLASH"
+CONFIG_NAND_BOOT=y
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 earlyprintk mtdparts=atmel_nand:256k(bootstrap)ro,512k(uboot)ro,256K(env),256k(env_redundant),256k(spare),512k(dtb),6M(kernel)ro,-(rootfs) rootfstype=ubifs ubi.mtd=7 root=ubi0:rootfs"