Refactoring of devices management

[ShadowCurse]

There have been several discussions about the way devices, device resources and device managers need to coexist in Firecracker.
Here are some links:

• Support for VMGenID device on x86 microVMs #4487 (comment)
• Add ACPI support for x86_64  #4428 (comment)
• Add ACPI support for x86_64  #4428 (comment)
• Add ACPI support for x86_64  #4428 (comment)
• Support for VMGenID device on x86 microVMs #4487 (comment)

Because device management is one of the key components in Firecracker we should think about the way to improve our code quality in this area as it will help us with future addition of new devices.

For now this issue can be just a hub for all thought about this topic.

Checks

• Have you searched the Firecracker Issues database for similar requests?
• Have you read all the existing relevant Firecracker documentation?
• Have you read and understood Firecracker's core tenets?