PCI: pnv_php: Enable third attention indicator state

The PCIe specification allows three attention indicator states, on, off,
and blink.  Enable all three states instead of basic on / off control.

This changes the userspace API (writes to the sysfs "attention" file) to
match the behavior of pciehp.  Here's the comparison of previous and new
indicator behavior:

  Value  Previous   New Behavior
  -----  --------   ------------------------
    0    off        (reserved, so undefined)
    1    on         on
    2    on         blink
    3    on         off

Signed-off-by: Timothy Pearson <tpearson@raptorengineering.com>
[bhelgaas: add specifics of behavior change]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/1210309411.1359866.1752615582001.JavaMail.zimbra@raptorengineeringinc.com