drm/i915: Update the helper to set correct mapping

Determine the possible coherent map type based on object location,
and if target has llc or if user requires an always coherent
mapping.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: CQ Tang <cq.tang@intel.com>
Suggested-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210427085417.120246-2-matthew.auld@intel.com