sb/intel/lynxpoint/acpi: Do not determine PCH type at runtime

Both PCH types are very different, and mixing the code for both together
isn't useful. Make `ISLP` return a constant, so that IASL can fold it.

Change-Id: I6222d6661115d444d4dad0217c2d376dc551465c
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45048
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/southbridge/intel/lynxpoint/acpi/pch.asl

@@ -7,11 +7,7 @@ Scope(\)
 	// Return TRUE if chipset is LynxPoint-LP
 	Method (ISLP, 0, NotSerialized)
 	{
-		If (LEqual (\_SB.PCI0.LPCB.DIDH, 0x9c)) {
-			Return (1)
-		} else {
-			Return (0)
-		}
+		Return (CONFIG(INTEL_LYNXPOINT_LP))
 	}
 
 	// IO-Trap at 0x800. This is the ACPI->SMI communication interface.