nv50,nvc0: clamp uniform size to 64k

nv50,nvc0: clamp uniform size to 64k

The state tracker will pass through requests from buggy applications
which will have the buffer size larger than the max allowed (64k). Clamp
the size to 64k so that we don't get errors when uploading the constbuf
data.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>