mb/starlabs/starbook/mtl: Set the MMIO Size to 3GiB

This is required when using 96GB of memory.

Change-Id: I3a2a3e737eeb9282a4edf09eb0a24019ceeb016e
Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86623
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/starlabs/starbook/variants/mtl/romstage.c

@@ -44,4 +44,5 @@ void mainboard_memory_init_params(FSPM_UPD *mupd)
 		mupd->FspmConfig.PcieRpEnableMask &= ~(1 << 8);
 
 	mupd->FspmConfig.PchHdaSubSystemIds = 0x70381e50;
+	mupd->FspmConfig.MmioSize = 0xb00;
 };