liquidio: make soft command calls synchronous

1. Add wait_for_sc_completion_timeout() for waiting the response and
   handling common response errors
2. Send sc's synchronously: remove unused callback function,
   and context structure; use wait_for_sc_completion_timeout() to wait
   its response.

Signed-off-by: Weilin Chang <weilin.chang@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>