devlink: add support for running selftests

devlink: add support for running selftests

Add commands and helper APIs to run selftests.
Include a selftest id for a non volatile memory i.e. flash.
Also, update the man page and bash-completion for selftests
commands.

Examples:
$ devlink dev selftests run pci/0000:03:00.0 id flash
pci/0000:03:00.0:
    flash:
      status passed

$ devlink dev selftests show pci/0000:03:00.0
pci/0000:03:00.0
      flash

$ devlink dev selftests show pci/0000:03:00.0 -j
{"selftests":{"pci/0000:03:00.0":["flash"]}}

$ devlink dev selftests run pci/0000:03:00.0 id flash -j
{"selftests":{"pci/0000:03:00.0":{"flash":{"status":"passed"}}}}

Signed-off-by: Vikas Gupta <vikas.gupta@broadcom.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>