freedreno/ir3: redirectable ir3 disasm output

freedreno/ir3: redirectable ir3 disasm output

For now it still goes to stdout, this will make it easier to support
output on stderr like what frameretrace expects.

(If we eventually have a proper GL extension for this, implementation
probably looks like dumping shader disasm to a tmp file and then dumping
that out over whatever mechanism is used.)

Signed-off-by: Rob Clark <robdclark@gmail.com>