devlink: add timeout information to status_notify

Add a timeout element to the DEVLINK_CMD_FLASH_UPDATE_STATUS
netlink message for use by a userland utility to show that
a particular firmware flash activity may take a long but
bounded time to finish.  Also add a handy helper for drivers
to make use of the new timeout value.

UI usage hints:
 - if non-zero, add timeout display to the end of the status line
 	[component] status_msg  ( Xm Ys : Am Bs )
     using the timeout value for Am Bs and updating the Xm Ys
     every second
 - if the timeout expires while awaiting the next update,
   display something like
 	[component] status_msg  ( timeout reached : Am Bs )
 - if new status notify messages are received, remove
   the timeout and start over

Signed-off-by: Shannon Nelson <snelson@pensando.io>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>