Move QEMU caps validation of QEMU_CAPS_OBJECT_USB_AUDIO and
QEMU_CAPS_DEVICE_ICH9_INTEL_HDA to a new function in qemu_domain.c,
qemuDomainDeviceDefValidateSound(). This function is called by
qemuDomainDeviceDefValidate() to validate the sound device
in domain define time.

qemuxml2xmltest.c was adjusted to add the now required caps for
domain definition.
Reviewed-by: NCole Robinson <crobinso@redhat.com>
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>