Fixed PCI device listing.

[MinusPL]

Fixes #129 Changes:

• Devices now have bus, device and function IDs
• Redesigned functions to read and write to PCI device configuration space
• Made sure devices return proper values from PCI config space.
• Added missing 192 bytes of device config space as union made of bytes, words and dwords. This region is device dependant.
• Limited reading of PCI config space to 64 bytes for PCI Bridges.
• Removed pci_in_data structure and replace it by pci_cmd_address_reg, which follows PCI specification naming.
• Added documentation for all PCI related functions.