In pwrite_fast, map an object page by page if obj_ggtt_pin fails. First,
we try a nonblocking pin for the whole object (since that is fastest if
reused), then failing that we try to grab one page in the mappable
aperture. It also allows us to handle objects larger than the mappable
aperture (e.g. if we need to pwrite with vGPU restricting the aperture
to a measely 8MiB or something like that).

v2: Pin pages before starting pwrite, Combined duplicate loops (Chris)

v3: Combined loops based on local patch by Chris (Chris)

v4: Added i915 wrapper function for drm_mm_insert_node_in_range (Chris)

v5: Renamed wrapper function for drm_mm_insert_node_in_range (Chris)

v5: Added wrapper for drm_mm_remove_node() (Chris)

v6: Added get_pages call before pinning the pages (Tvrtko)
Added remove_mappable_node() wrapper for drm_mm_remove_node() (Chris)

v7: Added size argument for insert_mappable_node (Tvrtko)

v8: Do not put_pages after pwrite, do memset of node in the wrapper
function (insert_mappable_node) (Chris)

v9: Rebase (Ankit)
Signed-off-by: NAnkitprasad Sharma <ankitprasad.r.sharma@intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>