IB/hfi1: Fix sdma_event_names[] build warning

sdma_event_names[] is only used within CONFIG_SDMA_VERBOSITY ifdefs, so
when CONFIG_SDMA_VERBOSITY is disabled, it results in the following
0-day build warning:
>> drivers/infiniband/hw/hfi1/sdma.c:137:27: warning: 'sdma_event_names'
>> defined but not used [-Wunused-const-variable=]
    static const char * const sdma_event_names[] = {
                              ^~~~~~~~~~~~~~~~
This occurs on the following compiler:
compiler: gcc-6 (Debian 6.1.1-1) 6.1.1 20160430

For more information check:
https://lists.01.org/pipermail/kbuild-all/2016-May/020060.html

Fix this warning by defining sdma_event_name[] only within the
CONFIG_SDMA_VERBOSITY ifdefs.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>