96boards: dragonboard/hikey: add device tree overlay support

96boards CE devices such as the DragonBoard and Hikey devices have numerous
mezzanine options some of which need overlays from the beginning so it makes
sense to enable device tree overlays.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>

configs/dragonboard410c_defconfig

@@ -37,3 +37,5 @@ CONFIG_USB_EHCI_MSM=y
 CONFIG_USB_ULPI_VIEWPORT=y
 CONFIG_USB_ULPI=y
 CONFIG_USB_STORAGE=y
+CONFIG_OF_LIBFDT=y
+CONFIG_OF_LIBFDT_OVERLAY=y

configs/hikey_defconfig

@@ -17,3 +17,5 @@ CONFIG_MMC_DW_K3=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_FAT_WRITE=y
+CONFIG_OF_LIBFDT=y
+CONFIG_OF_LIBFDT_OVERLAY=y