The option "-soundhw pcspk" gives me a error on PPC as follow:

qemu-system-ppc64: ISA bus not available for pcspk

This means this option doesn't work on ppc by default. So simply make
this an x86-specific option via identify_qemu_args().
Signed-off-by: NBoqun Feng <boqun.feng@gmail.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>