crypto: inside-secure - move request dequeueing into a workqueue

This patch moves the request dequeueing into a workqueue to improve the
coalescing of interrupts when sending requests to the engine; as the
engine is capable of having one single interrupt for n requests sent.
Using a workqueue allows to send more request at once.

Suggested-by: Ofer Heifetz <oferh@marvell.com>
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>