vc4: Fix sin(0.0) and cos(0.0) accuracy to fix SDL rendering rotation.

SDL has some shaders that compute sin(angle) and cos(angle) for a rotation
matrix in the VS, and angle is usually 0.0.  Our previous implementation
had quite a bit of error around 0.0, causing single-pixel rotations at
typical window sizes.  SDL2 has changed as of August 28th (commit
12156:e5a666405750) to not need sin/cos in the VS, but we should still fix
this for existing implementations or similar patterns that other programs
may have.

glsl-cos goes from 32 instructions to 36, but 9 uniforms to 7.
glsl-sin goes from 32 instructions to 34, but 8 uniforms to 7.

This seems like a fine impact to have for the bugfix.

Cc: 18.1 18.2 <mesa-stable@lists.freedesktop.org>
Fixes: https://github.com/anholt/mesa/issues/110
(cherry picked from commit 10d5d2d5)