meson: convert auto combos into proper features

Allows users to easily enable everything (eg. packagers or CI), or select just the drivers they want (eg. most people building it themselves) with something like:

-D auto-features=disabled -D amdgpu=enabled

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Note: features have been in meson since 0.47 and we already require 0.53, so there's no need to bump the minimum supported meson version.