ir3: use empirical size for params as used by the shader

ir3: use empirical size for params as used by the shader

For example only some UCPs may be used by the shader, triggering asserts
that too many consts are being uploaded.

While we're at it, also fix the const size when loading UCPs, since
otherwise it doesn't correspond to what the shader is actually using.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5752>