PCI: Add standard PCIe Capability Link ASPM field names

Add standard #defines for ASPM fields in PCI Express Link Capability and
Link Control registers.

Previously we used PCIE_LINK_STATE_L0S and PCIE_LINK_STATE_L1 directly, but
these are defined for the Linux ASPM interfaces, e.g.,
pci_disable_link_state(), and only coincidentally match the actual register
bits.  PCIE_LINK_STATE_CLKPM, also part of that interface, does not match
the register bit.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Acked-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>