i965/blorp: Use R16_UNORM for Z16 surfaces.

i965/blorp: Use R16_UNORM for Z16 surfaces.

Currently, all that matters is that we copy the correct number of bits,
so any format that has 16-bits of data will work fine.

Once BLORP begins handling format conversions, the sampler will need to
correctly interpret the data.  We don't need a depth format, but we do
need the right number of components and data type (UNORM).

For Z16, this means using R16_UNORM.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>