i965: Fix dump_prog_cache to handle compacted instructions.

i965: Fix dump_prog_cache to handle compacted instructions.

dump_prog_cache has interpreted compacted instructions as full size
instructions, decoding garbage and complaining about invalid values.

We can just use brw_dump_compile to handle this correctly in less code.
The output format changes slightly, but it's still perfectly acceptable.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>