Cleanup PCI passthrough code

Cleanup PCI passthrough code

The patch cleanups the code of PCI passthrough.

- Use LIST_FOREACH(). Don't use lh_first, le_next directly.
- Use pci_{read, write}_block instead of "switch(len) case [124]
  pci_{read, write}_{byte, word, long}();".
- Eliminate duplicate codes using PT_MEARGE_VALUE macro.
- Define PCI_ERR_* macro in pass-through.h if libpci is old.
- Remove the unreasonable loop from pt_aer_reg_{save,restore}.
- Enable pt_aer_reg_{save,restore}, even if libpci is old.
- Fix ro_mask and remove unnecessary pt_xxx_reg_write functions.
- Add "Error:" or "Warning:" to messages.
- Remove verbose messages.

Signed-off-by: Yuji Shimada <shimada-yxb@necst.nec.co.jp>