PCI/ASPM: Remove struct aspm_register_info.l1ss_ctl2 (unused)

We never use the aspm_register_info.l1ss_ctl2 value, so remove it.  No
functional change intended.

Link: https://lore.kernel.org/r/20201015193039.12585-9-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>