Implement S0ix low power states

[alice-sowerby]

User Story

As a laptop user I want to be able to use some functions of my laptop while it is in a low power state so that I can conserve battery charge and use the laptop for longer between charges.

NOTE: S0ix represents a set of SoC states which allow the SoC to consume less power by shutting off parts of the SoC when not needed. Source

Implementation Notes

There's an existing non-functional start of S0ix support, but nothing that is a demoable proof of concept.

Acceptance Criteria

• Targeting AMD initially
• Test on Intel (may work out of the box)