PCI/ASPM: Remove struct aspm_register_info.enabled

Previously we stored the "ASPM Control" bits from the Link Control register
in the struct aspm_register_info.

Read PCI_EXP_LNKCTL directly when needed.  This means we can use the
PCI_EXP_LNKCTL_ASPM_* bits directly instead of the similar but different
PCIE_LINK_STATE_* bits.  No functional change intended.

[bhelgaas: drop get_aspm_enable() and read LNKCTL once directly]
Link: https://lore.kernel.org/r/20201015193039.12585-6-helgaas@kernel.org


Signed-off-by: Saheed O. Bolarinwa <refactormyself@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>