IB/ehca: Fix eHCA driver compilation for uniprocessor

The eHCA driver does not compile for a uniprocessor configuration
(CONFIG_SMP=n), due to H_SUCCESS and other symbols being undefined.
This fixes it.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Hoang-Nam Nguyen <HNGUYEN@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>