nvc0: fix blit triangle size to fully cover FB's > 8192x8192

nvc0: fix blit triangle size to fully cover FB's > 8192x8192

The idea is that a single triangle will cover the whole area being
drawn, allowing the blit shader to do its work. However the max fb size
is 16384x16384, which means that the triangle we draw needs to be twice
that in order to cover the whole area fully. Increase the size of the
triangle to 32768x32768.

This fixes a number of dEQP tests that were failing because a blit was
involved which would miss some of the resulting texture.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "11.1 11.2" <mesa-stable@lists.freedesktop.org>