i965/fs: Manually generate the meta fast-clear shader

i965/fs: Manually generate the meta fast-clear shader

Previously, we were generating the fast-clear shader from GLSL.  The
problem is that fast clears require that we use a replicated write rather
than a regular write instruction.  In order to get this we had a
complicated and somewhat fragile optimization pass that looked for places
where we can use a replicated write and used it.  Since replicated writes
have a lot of restrictions, we only ever use them for fast-clear
operations.

This commit replaces the optimization pass with a function that just
generates the shader we want.  This is a) less code, b) less fragile than
the optimization pass, and c) generates a more efficient shader.

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>