- Remove drm_initmap and replace its usage with drm_addmap. This reduces

- Remove drm_initmap and replace its usage with drm_addmap. This reduces
    code duplication, and it also hands you the map pointer so you don't
    need to re-find it.
- Remove the permanent maps flag. Instead, for register and framebuffer
    maps, we always check whether there's already a map of that type and
    offset around. Move the Radeon map initialization into presetup (first
    open) so it happens again after every takedown.
- Remove the split cleanup of maps between driver takedown (last close) and
    cleanup (module unload). Instead, always tear down maps on takedown,
    and drivers can recreate them on first open.
- Make MGA always use addmap, instead of allocating consistent memory in
    the PCI case and then faking up a map for it, which accomplished nearly
    the same thing, in a different order. Note that the maps are exposed to
    the user again: we may want to expose a flag to avoid this, but it's
    not a security concern, and saves us a lot of code.
- Remove rmmaps in the MGA driver. Since the function is only called during
    takedown anyway, we can let them die a natural death.
- Make removal of maps happen in one function, which is called by both
    drm_takedown and drm_rmmap_ioctl.
Reviewed by: idr (previous revision) Tested on: mga (old/new/pci dma),
    radeon, savage