MIPS: Lantiq: Make it possible to build in no device tree

Now it is possible to build in no device tree at all and depend on the
boot loader providing one or someone concatenating a device tree to the
end of the image.

This was copied from arch/mips/bmips/Kconfig

Signed-off-by: Hauke Mehrtens <[e-mail]>
Acked-by: John Crispin <[e-mail]>
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/12899/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/lantiq/Kconfig

···
 endchoice
 
 choice
-	prompt "Devicetree"
+	prompt "Built-in device tree"
+	help
+	  Legacy bootloaders do not pass a DTB pointer to the kernel, so
+	  if a "wrapper" is not being used, the kernel will need to include
+	  a device tree that matches the target board.
+
+	  The builtin DTB will only be used if the firmware does not supply
+	  a valid DTB.
+
+config LANTIQ_DT_NONE
+	bool "None"
 
 config DT_EASY50712
 	bool "Easy50712"