drm/i915: Support appending to the rotated pages mapping
drm/i915: Support appending to the rotated pages mapping

By providing a start offset into the source array of pages, and returning the
end position in the scatter-gather table, we will be able to append the UV
plane to the rotated mapping in later patches.

v2: Rebase.

Signed-off-by: Tvrtko Ursulin <82325a91373a06cdf12f953d4611ffb7756aa8d4@intel.com>
Reviewed-by: Joonas Lahtinen <a11ca63949063c01fa551bf27c25e0fe898387c4@linux.intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs