import latest DTS files

Kia ora koutou,
I'm having a go at importing the latest DTS sources from kernel.org
into my -current source tree so that I can get the latest DTS files for
my Jetson Nano.

There seem to be some significant problems with the Linux code though. 

The biggest problem is a recent way the Linux people have been adding
support for board variants. Here is an example.

A few months back DTS files were added for something called a Freebox
containing an Amlogic Meson. There seem to be two variants of this
board with either a Broadcom or Realtek Bluetooth chip. The DTS files
are implemented as the following three files.

  * meson-g12a-fbx8am.dts
  * meson-g12a-fbx8am-brcm.dtso
  * meson-g12a-fbx8am-realtek.dtso

i.e. the board differences have been factored out into overlays. Fine,
whatever.

The Makefile code the Linux folks have added is this.

	dtb-$(CONFIG_ARCH_MESON) += meson-g12a-fbx8am-brcm.dtb
	dtb-$(CONFIG_ARCH_MESON) += meson-g12a-fbx8am-realtek.dtb
	
	# Overlays
	meson-g12a-fbx8am-brcm-dtbs     := meson-g12a-fbx8am.dtb
meson-g12a-fbx8am-brcm.dtbo
	meson-g12a-fbx8am-realtek-dtbs  := meson-g12a-fbx8am.dtb
meson-g12a-fbx8am-realtek.dtbo

The Linux Makefile in linux-6.9.6/scripts/Makefile.lib seems to know
how to glue all this together and build all the named files, including
merging the overlay and the base DTB into single DTB AFAICT. 

Have we dealt with this before? 

Ngā mihi,
Lloyd