staging: vchiq_arm: rework probe and init functions

Moves the allocation of a chardev region and class creation to the init
function of the driver since those functions are meant to be run on a
per driver basis, as opposed to the code run in the probe function which
is run in a per device basis.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>