staging: wilc1000: Replace kthread with workqueue for host interface

Deconstruct the kthread / message_queue logic, replacing it with
create_singlethread_workqueue() / queue_work() setup, by adding a
'struct work_struct' to 'struct host_if_msg'. The current kthread
hostIFthread() is converted to a work queue helper with the name
'host_if_work'.

Signed-off-by: Binoy Jayan <binoy.jayan@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>