#defines. This also has the advantage that it makes the names more
compact, iand also allows us to correct the non-uniform naming of
the PCIM_LINK_* defines, making them all consistent amongst themselves.
This is a mostly mechanical rename:
s/PCIR_EXPRESS_/PCIER_/g
s/PCIM_EXP_/PCIEM_/g
s/PCIM_LINK_/PCIEM_LINK_/g
When this is MFC'd, #defines will be added for the old names to assist
out-of-tree drivers.
Discussed with: jhb
MFC after: 1 week