nb/intel/i945: Make pci_mmio_size a devicetree parameter

Instead of hardcoding pci_mmio_size in the raminit code,
this makes it a parameter in the devicetree.

A safe minimum of 768M is also defined since using anything
less causes problems (if 4G of ram is used).

Change-Id: If004c861464162d5dbbc61836a3a205d1619dfd5
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/16856
Tested-by: build bot (Jenkins)
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/src/northbridge/intel/i945/chip.h b/src/northbridge/intel/i945/chip.h
index 446af72..8eaa5b4 100644
--- a/src/northbridge/intel/i945/chip.h
+++ b/src/northbridge/intel/i945/chip.h
@@ -8,6 +8,7 @@
 	u32 gpu_backlight;
 	int gpu_lvds_use_spread_spectrum_clock;
 	struct i915_gpu_controller_info gfx;
+	int pci_mmio_size;
 };
 
 #endif /* NORTHBRIDGE_INTEL_I945_CHIP_H */