configs/beaglev_fire: add support for overlays and update script

When applying overlays at boot time all dtbs need to be compiled with
the `-@` flag. Set the appropriate config to do this.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jamie Gibbons <jamie.gibbons@microchip.com>
Signed-off-by: Romain Naour <romain.naour@smile.fr>

configs/beaglev_fire_defconfig

@@ -12,6 +12,7 @@ BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="$(call github,linux4microchip,linux,li
 BR2_LINUX_KERNEL_DEFCONFIG="mpfs"
 BR2_LINUX_KERNEL_DTS_SUPPORT=y
 BR2_LINUX_KERNEL_INTREE_DTS_NAME="microchip/mpfs-beaglev-fire"
+BR2_LINUX_KERNEL_DTB_OVERLAY_SUPPORT=y
 BR2_PACKAGE_MTD=y
 BR2_TARGET_ROOTFS_EXT2=y
 BR2_TARGET_ROOTFS_EXT2_4=y