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/sama5d4_xplained_mmc_defconfig b/configs/sama5d4_xplained_mmc_defconfig
index ffc01f4..dabbf60 100644
--- a/configs/sama5d4_xplained_mmc_defconfig
+++ b/configs/sama5d4_xplained_mmc_defconfig
@@ -13,7 +13,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="at91-sama5d4_xplained"
 CONFIG_DEBUG_UART=y
 CONFIG_FIT=y
-CONFIG_SYS_EXTRA_OPTIONS="SAMA5D4,SYS_USE_MMC"
+CONFIG_SD_BOOT=y
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 earlyprintk root=/dev/mmcblk0p2 rw rootwait"