skl mainboards: Move cpu_cluster device to chipset devicetree

Change-Id: I7114612e686a0bf3cfc241f45fa62077fad16f5a
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83161
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/system76/kbl-u/devicetree.cb

@@ -105,8 +105,6 @@ chip soc/intel/skylake
 		.dc_loadline = 310,
 	}"
 
-	device cpu_cluster 0 on end
-
 	device domain 0 on
 		device ref system_agent on end
 		device ref igpu on end