haven: rm: Send requests atomically to RM

RM core driver can send out multiple requests in parallel to RM, e.g.
00111002302222113456111 (numbers indicate seq-id, and the recursion of a
number indicates fragments). RM can only process one request at a time
and would reject any messages unrelated to the request it was first
receiving. Thus, add a lock to enforce requests are sent sequentially.

Change-Id: I1e75dd40d7b8bf47ca4120f33c70f1ee452ba7b1
Signed-off-by: Elliot Berman <eberman@codeaurora.org>