devlink: add support for DEVLINK_CMD_REGION_NEW

devlink: add support for DEVLINK_CMD_REGION_NEW

Add support to request that a new snapshot be taken immediately for
a devlink region. To avoid confusion, the desired snapshot id must be
provided.

Note that if a region does not support snapshots on demand, the kernel
will reject the request with -EOPNOTSUP.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>