Add support for 3 TDX subfeatures

Support is requested for 3 TDX-specific features:

 - Unaccepted memory, aka "lazy memory accept"
 - TDX "Get Quote" - is needed for attestation
 - Marking the TSC as reliable

More information at: https://canonical.lightning.force.com/lightning/r/Case/5008e00000FTWGcAAP/view

Testing:
Intel has provided code review for the first 2 and has additionally tested the GetQuote feature.
GCP has tested all three features and confirmed basic functionality and sanity. More testing will follow when the changes are available in -proposed and before feature release.

Regression potential:
Most of the code changes are to the following files:

arch/x86/coco/tdx
drivers/virt/coco/tdx-guest/tdx-guest.c
mm/memblock.c
mm/memory_hotplug.c
mm/page_alloc.c
mm/vmstat.c

Most of it is new code which is inside #ifdef CONFIG_UNACCEPTED_MEMORY

There is 1 tree-wide change "mm, treewide: redefine MAX_ORDER sanely" that affects many files and looks scary, but should be safe as it is basically a refactor.

Generally speaking, the code changes here affect early memory initialization on x86 so can impact anything in that area, but realistically should only affect TDX instances (especially ones with >4GB as that is when the unaccepted-memory feature is activated).