powerpc/eeh: Set attention indicator while recovering

I am the RAS team. Hear me roar.

Roar.

On a more serious note, being able to locate failed devices can be helpful.
Set the attention indicator if the slot supports it once we've determined
the device is present and only clear it if the device is fully recovered.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190903101605.2890-12-oohall@gmail.com