radeonsi: workaround for tesselation on SI

radeonsi: workaround for tesselation on SI

We request more than 32KB of LDS here, which SI doesn't have. Since LLVM
recently started checking the size of declared LDS allocations, all shaders
involved in tesselation fail to compile on SI.

Note that the entire calculation here seems wrong, given how we calculate
indices for generic attributes, so the number ends up wrong on CI+ as well.
A proper solution is clearly needed, but this patch should serve as a band-aid
for SI in the meantime.

Also note that the real size of the LDS allocation in hardware is independent
from what we tell LLVM, so this is really more of a "cosmetic" change.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95198
Cc: "11.2" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>