i965: Use a uniform for gl_PatchVerticesIn in the TCS on Gen8+.

i965: Use a uniform for gl_PatchVerticesIn in the TCS on Gen8+.

We still need to recompile the passthrough shader when this value
changes, as it also affects the output vertex count.  But otherwise,
we can eliminate recompiles on Gen8+.

We probably want to do this for Gen7 as well, but that requires
rewriting the input release code to use a loop, which is a trade-off
I'd need to consider in more detail.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Cc: mesa-stable@lists.freedesktop.org
(cherry picked from commit c319512e16f19bf1f558670981bbb4af510ba9f4)