staging: vc04_services: Add vchi_queue_user_message function

The vchi_msg_queue function which is used by other drivers
to queue a message is difficult to understand and overly
generic.

Add a new function which is a wrapper on top of vchi_msg_queue
that is specifically for queuing a message located in user
address space.

int
vchi_queue_user_message(VCHI_SERVICE_HANDLE_T handle,
                        void __user *data,
                        unsigned int size)

Signed-off-by: Michael Zoran <mzoran@crowfest.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>