drm/i915 + agp/intel-gtt: prep work for direct setup

To be able to directly set up the intel-gtt code from drm/i915 and
avoid setting up the fake-agp driver we need to prepare a few things:
- pass both the bridge and gpu pci_dev to the probe function and add
  code to handle the gpu pdev both being present (for drm/i915) and
  not present (fake agp).
- add refcounting to the remove function so that unloading drm/i915
  doesn't kill the fake agp driver

v2: Fix up the cleanup and refcount, noticed by Jani Nikula.

Reviewed-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/intel-gtt.h

@@ -23,6 +23,10 @@ const struct intel_gtt {
 	phys_addr_t gma_bus_addr;
 } *intel_gtt_get(void);
 
+int intel_gmch_probe(struct pci_dev *bridge_pdev, struct pci_dev *gpu_pdev,
+		     struct agp_bridge_data *bridge);
+void intel_gmch_remove(void);
+
 void intel_gtt_chipset_flush(void);
 void intel_gtt_unmap_memory(struct scatterlist *sg_list, int num_sg);
 void intel_gtt_clear_range(unsigned int first_entry, unsigned int num_entries);