nb/intel/x4x: Increase MMIO PCI space to 2GiB

This is necessary for PCI express graphics card add-ons,
otherwise the pci allocator cannot fit the mmio for the
add on card into the space it has available and the OS
turns off the card.  Old value was 1GiB.

Change-Id: I606994501b15e636fe209d1ed4b3d3f73b42bf5c
Signed-off-by: Damien Zammit <damien@zamaudio.com>
Reviewed-on: https://review.coreboot.org/16494
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/northbridge/intel/x4x/raminit_ddr2.c

@@ -1633,7 +1633,7 @@ static void mmap_ddr2(struct sysinfo *s)
 	gfxsize = ggc2uma[(ggc & 0xf0) >> 4];
 	gttsize = ggc2gtt[(ggc & 0xf00) >> 8];
 	tsegsize = 1; // 1MB TSEG
-	mmiosize = 0x400; // 1GB MMIO
+	mmiosize = 0x800; // 2GB MMIO
 	tom = s->channel_capacity[0] + s->channel_capacity[1] - ME_UMA_SIZEMB;
 	tolud = MIN(0x1000 - mmiosize, tom);