intel: Remove the pbo zero-copy code.

intel: Remove the pbo zero-copy code.

There were notes about the possibility of slowdowns due to zcopy from
a PBO due to thrashing around of the region.  Slowdowns are even more
likely now that textures are generally tiled, which a zcopy wouldn't
get.  Additionally, there were no checks on the buffer size to ensure
that the hardware-required rounding was present, which could result in
GPU hangs on large zcopy PBOs.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>