cpu/intel/sandybridge: Use enum for ACPI C states

Also remove the now unnecessary comments from the devicetree.

Change-Id: Iebbe12fd413b7a2eb1078a579e194eba821ada7c
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69292
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/mainboard/samsung/stumpy/devicetree.cb b/src/mainboard/samsung/stumpy/devicetree.cb
index ea164c4..cd7b907 100644
--- a/src/mainboard/samsung/stumpy/devicetree.cb
+++ b/src/mainboard/samsung/stumpy/devicetree.cb
@@ -17,8 +17,8 @@
 			device lapic 0 on end
 			device lapic 0xacac off end
 
-			register "acpi_c1" = "3"	# ACPI(C1) = MWAIT(C3)
-			register "acpi_c2" = "4"	# ACPI(C2) = MWAIT(C6)
+			register "acpi_c1" = "CPU_ACPI_C3"
+			register "acpi_c2" = "CPU_ACPI_C6"
 		end
 	end