PCI framework refactor: part 1

[AnErrupTion]

Howdy! This PR is the first part of refactoring the PCI subsystem in the device driver framework to increase code readability and thus decrease code "spaghettiness". Here are the changes done in this first part:

• Remove IPCIControllerLegacy because it was unused
• Remove PCIDeviceConfiguration because it was only used by the PCIControllerService and the PCIDeviceService
• Added a constructor in the PCIDevice class a constructor which allows setting the bus, slot and function of the device
• The PCICommand and the PCIConfigurationHeader structs have been split from the PCIDevice class
• The DeviceService.Initialize() method was added to initialize generic device drivers
• The PCIControllerService and the PCIDeviceService were merged into one service