radeonsi: Store inputs to memory when not using a TCS.

radeonsi: Store inputs to memory when not using a TCS.

We need to copy the VS outputs to memory. I decided to do this
using a shader key, as the value depends on other shaders.

I also switch the fixed function TCS over to monolithic, as
otherwisze many of the user SGPR's need to be passed to the
epilog, which increases register pressure, or complexity to
avoid that. The main body of the fixed function TCS is not
that interesting to precompile anyway, since we do it on
demand and it is very small.

v2: Use u_bit_scan64.

Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>