gallium/tests/trivial: Import compute unit tests.

gallium/tests/trivial: Import compute unit tests.

Add a test program that tries to exercise some of the language
features commonly used by compute programs at the Gallium API level:

   - Correctness of the values returned by the grid parameters.
   - Proper functioning of resource LOADs and STOREs.
   - Subroutine calls.
   - Argument passing to the compute parameter through the INPUT
     memory space.
   - Mapping of buffer objects to the GLOBAL memory space.
   - Proper functioning of the PRIVATE and LOCAL memory spaces.
   - Texture sampling and constant buffers.
   - Support for multiple kernels in the same program.
   - Indirect resource indexing.
   - Formatted resource loads and stores (i.e. with channel conversion
     and scaling) using several different formats.
   - Proper functioning of work-group barriers.
   - Atomicity and semantics of the atomic opcodes.

As of now all of them seem to pass on my nvA8.