Doig a full clean up from mga_do_dma_bootstrap when

    mga_do_agp_dma_bootstrap fails causes problems if
    mga_do_pci_dma_bootstrap succeeds. This commit makes it possible to do
    a "minimal" clean up instead. I'm still trying to figure out what is
    causing the failures in mga_do_agp_dma_bootstrap...
Signed-off-by: Ian Romanick <idr@us.ibm.com>