sb/intel/i82801ix: Add common code to set up LPC IO decode ranges

This does the following:
- Add gen[1-4]_dec options to the devicetree to set up generic LPC
  decode ranges in the southbridge code.
- Move setting up some default decode ranges to a common place. If
  somehow a board needs to override this behavior it can happen in the
  mb_setup_superio() hook (that will be renamed when moving to
  C_ENVIRONMENT_BOOTBLOCK).

Change-Id: I3d904b1125bc410c11aa73a89b1969284e88dac1
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35991
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/src/mainboard/lenovo/t400/devicetree.cb b/src/mainboard/lenovo/t400/devicetree.cb
index b4c2ea8..9561dfa 100644
--- a/src/mainboard/lenovo/t400/devicetree.cb
+++ b/src/mainboard/lenovo/t400/devicetree.cb
@@ -75,6 +75,9 @@
 			# Maybe we should set less for Mini PCIe.
 			register "pcie_power_limits" = "{ { 10, 0 }, { 10, 0 }, { 0, 0 }, { 10, 0 }, { 0, 0 }, { 0, 0 } }"
 			register "pcie_hotplug_map" = "{ 0, 0, 0, 1, 0, 0, 0, 0 }"
+			register "gen1_dec" = "0x007c1601"
+			register "gen2_dec" = "0x000c15e1"
+			register "gen3_dec" = "0x001c1681"
 
 			device pci 19.0 on end # LAN
 			device pci 1a.0 on # UHCI