gallium: Add support for 32x32 muls with 64 bit results

gallium: Add support for 32x32 muls with 64 bit results

The code introduces two new 32bit integer multiplication opcodes which
can be used to produce correct 64 bit results. GLSL, OpenCL and D3D10+
require them. We use two seperate opcodes, because they match the
behavior of GLSL and OpenCL, are a lot easier to add than a single
opcode with multiple destinations and because there's not much (any)
difference wrt code-generation.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: José Fonseca <jfonseca@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>