agp: switch AGP to use page array instead of unsigned long array

agp: switch AGP to use page array instead of unsigned long array

This switches AGP to use an array of pages for tracking the
pages allocated to the GART. This should enable GEM on PAE to work
a lot better as we can pass highmem pages to the PAT code and it will
do the right thing with them.

Signed-off-by: Dave Airlie <airlied@redhat.com>