nb/intel/sandybridge: Add a chipset devicetree

This only moves CPU configuration to a common place. Other PCI devices
can be done in follow-ups.

Change-Id: I9c5b6f25b779e28b6719cf70455ff0f1a916ad87
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56912
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/sandybridge/Kconfig

@@ -17,6 +17,9 @@ config NORTHBRIDGE_SPECIFIC_OPTIONS
 	select NO_DDR2
 	select USE_DDR3
 
+config CHIPSET_DEVICETREE
+	default "northbridge/intel/sandybridge/chipset.cb"
+
 config SANDYBRIDGE_VBOOT_IN_ROMSTAGE
 	bool
 	default n

src/northbridge/intel/sandybridge/chipset.cb

@@ -0,0 +1,18 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+chip northbridge/intel/sandybridge
+	device cpu_cluster 0 on
+		chip cpu/intel/model_206ax
+			# Magic APIC ID to locate this chip
+			device lapic 0 on end
+			device lapic 0xacac off end
+
+			register "acpi_c1" = "1"	# ACPI(C1) = MWAIT(C1)
+			register "acpi_c2" = "3"	# ACPI(C2) = MWAIT(C3)
+			register "acpi_c3" = "5"	# ACPI(C3) = MWAIT(C7)
+		end
+	end
+
+	device domain 0 on
+	end
+end