PCI/DPC: Remove unnecessary RP PIO register structs

We read and immediately print the RP PIO log registers.  We don't save
them, so there's no need to define structs for them.  Remove the structs
and read the registers into local variables instead.  No functional change
intended.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sinan Kaya <okaya@codeaurora.org>