i965/blorp: Add support for sampling 3D textures

i965/blorp: Add support for sampling 3D textures

This patch adds additional MOV instruction for all blorp programs
that use SHADER_OPCODE_TXF. Alternative is to augment blorp program
key to tell if z-coordinate is needed, add condition to the blorp
blit compiler and to produce a variant with and without the MOV.
This seems a little overkill.

Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>