drm/i915: support 2M pages for the 48b PPGTT

drm/i915: support 2M pages for the 48b PPGTT

Support inserting 2M gtt pages into the 48b PPGTT.

v2: sanity check sg->length against page_size

v3: don't recalculate rem on each loop
    whitespace breakup

Signed-off-by: Matthew Auld <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Chris Wilson <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]