sb/intel/i82801gx,ix: Drop MPEN from GNVS

It's a static value that is neither referenced from SMI handler
nor needs to be updated on S3 resume path.

Change-Id: I3928e5973fe65d9a4fe7975e5d5584efe6e5f2f8
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50120
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/cpu/intel/speedstep/acpi.c

@@ -133,4 +133,8 @@ void generate_cpu_entries(const struct device *device)
 	acpigen_write_processor_package("PPKG", 0, cores_per_package);
 
 	acpigen_write_processor_cnot(cores_per_package);
+
+	acpigen_write_scope("\\");
+	acpigen_write_name_integer("MPEN", numcpus > 1);
+	acpigen_pop_len();
 }

src/cpu/intel/speedstep/acpi/cpu.asl

@@ -5,6 +5,7 @@ External (\_SB.CNOT, MethodObj)
 External (\_SB_.CP00, DeviceObj)
 External (\_SB_.CP00._PPC)
 External (\_SB_.CP01._PPC)
+External (\MPEN, IntObj)
 
 Method (PNOT)
 {