dts: meson: Switch GXL, GXM & AXG to using upstream DT

dts: meson: Switch GXL, GXM & AXG to using upstream DT

Enable OF_UPSTREAM to use upstream DT and add amlogic/ prefix to the
DEFAULT_DEVICE_TREE. And thereby directly build DTB from dts/upstream/src/
including *-u-boot.dtsi files from arch/$(ARCH)/dts/ directory.

Cc: Sumit Garg <[email protected]>
Acked-by: Viacheslav Bocharov <[email protected]>
Reviewed-by: Sumit Garg <[email protected]>
Tested-by: Mattijs Korpershoek <[email protected]> # khadas-vim3_android
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Neil Armstrong <[email protected]>