MycroftOS: Split vc4 overlay loading for pi3 and pi4

buildroot-external/board/raspberrypi/config.txt

@@ -3,7 +3,13 @@
 # You should override this file using a post-build script.
 # See http://buildroot.org/manual.html#rootfs-custom
 # and http://elinux.org/RPiconfig for a description of config.txt syntax
+[pi3]
+dtoverlay=vc4-kms-v3d
 
+[pi4]
+dtoverlay=vc4-kms-v3d-pi4
+
+[all]
 # We always use the same names, the real used variant is selected by
 # BR2_PACKAGE_RPI_FIRMWARE_{DEFAULT,X,CD} choice
 start_file=start.elf
@@ -20,7 +26,6 @@ disable_overscan=1
 hdmi_group=1
 hdmi_mode=4
 max_framebuffers=2
-dtoverlay=vc4-kms-v3d
 
 # uncomment if you get no picture on HDMI for a default "safe" mode
 # hdmi_safe=1