PCI framework refactor: part 2

[AnErrupTion]

This PR is the second part of #1212 and focuses on more changes within the PCI subsystem. The following changes were done:

• The ISABus device driver was removed in favor of an ISADeviceService
• Added PCIField.All to include all fields in the enum at once
• Added a BusType property in Device, which is set to the DeviceDriverRegistryEntry's BusType by default
• In PCIDevice:
  • The PCI controller field was made public
  • Properties like VendorID and DeviceID are now retrieved once
• DeviceDriverRegistryEntry.Factory is now checked for nullability, and same for the BaseDeviceDriver instantiated by it
• Added the DeviceService.GetAllDevices(DeviceBusType) method as a way to get all devices by a specific bus type, e.g. ISA or PCI. This unifies the process, instead of having to check for ISABus or PCIDevice respectively
• In PCIDeviceService:
  • The service no longer relies on events to initialize PCI devices. Instead, the code was moved in the Initialize() method, where it finds for the first initialized IPCIController
  • In case no matched driver entry is found, a fallback bus type is set in the Device. This allows for retrieving unknown PCI devices using the newly added DeviceService.GetAllDevices(DeviceBusType) method, instead of getting all devices that inherit from PCIDevice

[tgiphil]

Note: There are lots of other types of busses.