drm/i915: move engine scratch to LMEM

Prefer allocating the engine scratch from LMEM on dgfx.

v2: flatten the chain

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210127131417.393872-7-matthew.auld@intel.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>