MFC r200764
MFC r200764

Fix a handful of issues with via agp support.

  * Read the pci capability register to identify AGP 3 support
  * Add missing smaller aperture sizes for AGP3 chips.
  * Fix the aperture size calculation on AGP2 chips.
    All sizes between 32M and 256M reported as 256M.
  * Add \n to error string.

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