sb/intel/i82801gx: Add common LPC decode code

Generic LPC decode ranges can now be set from the devicetree.

Change-Id: I1065ec770ad3a743286859efa39dca09ccb733a1
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36700
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/src/mainboard/asus/p5gc-mx/devicetree.cb b/src/mainboard/asus/p5gc-mx/devicetree.cb
index 972dc5d..b5409a2 100644
--- a/src/mainboard/asus/p5gc-mx/devicetree.cb
+++ b/src/mainboard/asus/p5gc-mx/devicetree.cb
@@ -55,6 +55,9 @@
 
 			register "p_cnt_throttling_supported" = "0"
 
+			# SuperIO Power Management Events
+			register "gen1_dec" = "0x00040291"
+
 			device pci 1b.0 on # High Definition Audio
 				ioapic_irq 2 INTA 0x10
 			end