drm/i915: Use helper func to find out map type

Use i915_coherent_map_type() function to find out
map_type of the shmem obj.

v2: handle non-llc platform(Matt)

Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221219112933.21417-1-nirmoy.das@intel.com