drm/radeon/kms: add more elaborate benchmarks

Lots of new (and hopefully useful) benchmark. Load the driver
with radeon_benchmark=<test_number> and enjoy. Among tests
added are VRAM to VRAM blits and blits with buffer size sweeps.
The latter can be from GTT to VRAM, VRAM to GTT, and VRAM to VRAM
and there are two types of sweeps: powers of two and (probably
more interesting) buffers sizes that correspond to common modes.

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>