devlink: support direct region read requests

devlink: support direct region read requests

The kernel has gained support for reading from regions without needing to
create a snapshot. To use this support, the DEVLINK_ATTR_REGION_DIRECT
attribute must be added to the command.

For the "read" command, if the user did not specify a snapshot, add the new
attribute to request a direct read. The "dump" command will still require a
snapshot. While technically a dump could be performed without a snapshot it
is not guaranteed to be atomic unless the region size is no larger than
256 bytes.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David Ahern <dsahern@kernel.org>