drm/i915/uapi: add NEEDS_CPU_ACCESS hint

drm/i915/uapi: add NEEDS_CPU_ACCESS hint

If set, force the allocation to be placed in the mappable portion of
I915_MEMORY_CLASS_DEVICE. One big restriction here is that system memory
(i.e I915_MEMORY_CLASS_SYSTEM) must be given as a potential placement for the
object, that way we can always spill the object into system memory if we
can't make space.

Testcase: igt@gem-create@create-ext-cpu-access-sanity-check
Testcase: igt@gem-create@create-ext-cpu-access-big
Signed-off-by: Matthew Auld <[email protected]>
Cc: Thomas Hellström <[email protected]>
Cc: Lionel Landwerlin <[email protected]>
Cc: Jon Bloomfield <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Jordan Justen <[email protected]>
Cc: Kenneth Graunke <[email protected]>
Cc: Akeem G Abodunrin <[email protected]>
Reviewed-by: Nirmoy Das <[email protected]>
Reviewed-by: Thomas Hellström <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]