Add support for AMD-based hosts

[crawfxrd]

Add initial support for AMD-based hosts. Some of the work includes:

• Gate Intel-specific interfaces that are unconditionally included
• Add support for SB-TSI for reading host temp
• Refactor power module to handle different SoC flows

Also consider:

• Rework existing dGPU support for differentiating NVIDIA and AMD GPUs

Ref: https://github.com/system76/firmware-open/issues/196