This patch makes a couple of changes in the way the driver uses the
"get capabilities" command.

1. Get device capabilities in addition to function capabilities

2. Align to latest spec by using cap_count to determine size of the
   buffer in case of length error.
Signed-off-by: NAnirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>