radeonsi: add GS multiple streams support (v2)

radeonsi: add GS multiple streams support (v2)

This is the final piece for ARB_gpu_shader5,

The code is based on the r600 code from Glenn Kennard,
and myself.

While developing this, I'm not 100% sure of all the calculations
made in the GS registers, this is why the max_stream is worked
out there and used to limit the changes in registers. Otherwise
my initial attempts either regressed GS texelFetch tests
or primitive-id-restart. The current code has no regressions
in piglit.

This commit doesn't enable ARB_gpu_shader5, since that just
bumps the glsl level to 4.00, so I'll just do a separate patch
for 4.10.

v1.1: fix bug introduced in rebase.
v2: Address Marek's review comments,
remove my llvm stream code for simpler C,
move gsvs_ring and gs_next_vertex to arrays.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>