disas: arm-a64: Make printfer and stream variable

disas: arm-a64: Make printfer and stream variable

In a normal disassembly flow, the printf() and stream being used varies
from disas job to job. In particular it varies if mixing monitor_disas
and target_disas.

Make both the printf() function and target stream settable in the
QEMUDisassmbler class.

Reviewed-by: Claudio Fontana <claudio.fontana@huawei.com>
Tested-by: Claudio Fontana <claudio.fontana@huawei.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>