Instead of adding a new function for each capability added, introduce a
generic helper to query device capabilities.

Link: https://lore.kernel.org/r/20200731060420.17053-2-galpress@amazon.comReviewed-by: Firas JahJah <firasj@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>