Added device_is_agp callback to drm_driver. This function is called by the

    platform-specific drm_device_is_agp function. Added implementation of
    this function the the Linux-specific portion of the MGA driver to
    detect PCI G450 cards. Added code to the Linux-specific portion of the
    generic DRM layer to not initialize AGP infrastructure if the card is
    not AGP (this matches what already existed in BSD).
Bumped the driver date and the driver patch-level for MGA.
This mostly fixes bugzilla #3248. The BSD side still needs an
    implementation of mga_driver_device_is_agp.