staging: vchiq_arm: Register a platform device for audio

Following Eric's commit 37b7b308 ("staging/vc04_services: Register a
platform device for the camera driver.") this register the audio driver as
a platform device, too.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>