i965/fs: allow unit tests to dump the final patched assembly

i965/fs: allow unit tests to dump the final patched assembly

Unit tests comparing generated blorp programs to known good need
to have the dump in designated file instead of in default
standard output. The comparison also expects the jump counters
of if-else-instructions to be correctly set and hence the dump
needs to be taken _after_ 'patch_IF_ELSE()' is run (the default
dump of the fs_generator does this before).

v2 (Paul): dropped the redundant 'dump_enabled' argument

Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>