intel: Extend the force_y_tiling flag to allow forcing no tiling.

intel: Extend the force_y_tiling flag to allow forcing no tiling.

For a blit-uploaded temporary, it's faster on current hardware to memcpy
the data into a linear CPU mapping than to go through the GTT.

v2: Turn the not-fully-supported mask into 3 supported enum values.

Reviewed-and-tested-by: Ian Romanick <ian.d.romanick@intel.com> (v1)
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> (v1)
Reviewed-by: Paul Berry <stereotype441@gmail.com> (v2)
Reviewed-by: Chad Versace <chad.versace@linux.intel.com> (v2)