i965: Rename brw_{fs,vec4}_emit.cpp to brw_{fs,vec4}_generator.cpp.

i965: Rename brw_{fs,vec4}_emit.cpp to brw_{fs,vec4}_generator.cpp.

The previous names were really confusing to talk about:
- brw_fs_visitor() contained methods named emit_whatever().
- brw_fs_generator() contained methods named generate_whatever(), but
  lived in brw_fs_emit.cpp.

So when someone said "the emit layer", or "emit code", we weren't sure
whether they meant the visitor's emit() functions or the generator in
brw_fs_emit.cpp.

By renaming these files, the method names, class names, and file names
all match, which is much less confusing.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Paul Berry <stereotype441@gmail.com>
Acked-by: Eric Anholt <eric@anholt.net>