This API sucks.  Fortunately it's mostly unused at this point.  geode,
sis, and xgi need minor patches to use the corresponding pciaccess code,
neomagic will (more explicitly) lose its non-PCI support, and newport
will need to be ported to /dev/mem or the platform bus or something.

This should also make it pretty clear that alpha's sparse memory support
was basically not a thing anymore, very few tears shed.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Adam Jackson <ajax@redhat.com>