configs: sama5d3_xplained: add fdt overlay support

Add commands for fdt overlay merging. This is required for the boot scripts
that detect PDAs and apply specific overlays to the DTB passed on to kernel.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
diff --git a/configs/sama5d3_xplained_mmc_defconfig b/configs/sama5d3_xplained_mmc_defconfig
index 7d8d1ad..154cdc2 100644
--- a/configs/sama5d3_xplained_mmc_defconfig
+++ b/configs/sama5d3_xplained_mmc_defconfig
@@ -80,3 +80,4 @@
 CONFIG_W1_GPIO=y
 CONFIG_W1_EEPROM=y
 CONFIG_W1_EEPROM_DS24XXX=y
+CONFIG_OF_LIBFDT_OVERLAY=y