x86/virt/tdx: Allocate page bitmap for Dynamic PAMT

The TDX Physical Address Metadata Table (PAMT) holds data about the
physical memory used by TDX, and must be allocated by the kernel during
TDX module initialization.

The exact size of the required PAMT memory is determined by the TDX module
and may vary between TDX module versions. Currently it is approximately
0.4% of the system memory. This is a significant commitment, especially if
it is not known upfront whether the machine will run any TDX guests.

Each memory region that the TDX module might use needs three separate PAMT
allocations. One for each supported page size (1GB, 2MB, 4KB). The
TDX module supports a new feature designed to reduce PAMT overhead called
Dynamic PAMT (DPAMT). Under DPAMT the 4KB level is allocated dynamically
during runtime, while the 1GB and 2MB levels remain allocated on TDX
module initialization.

However, in the details, DPAMT still needs some smaller per 4KB page
scoped data (currently it is 1 bit per page). The TDX module exposes the
number of bits as a separate piece of metadata than the 4KB static
allocation for normal PAMT. Although the size is enumerated differently,
it is handed to the TDX module in the same way the 4KB page size PAMT
allocation is for normal PAMT.

Begin to implement DPAMT in the kernel by reading the bits-per-page needed
for DPAMT. Calculate the size needed for the bitmap, and use it instead of
the 4KB size determined for normal PAMT, in the case of DPAMT.

The existing metadata reading code was generated by a script, but the
current plan is to stop generating this code, as the script has continued
to need adjustments. So add manually written code and adjust the comment
about it being autogenerated to be more generic. Start to adopt a more
normal kernel code style without the ternary statements and if
conditionals assignments that the auto generated code has.

AI was used under supervision to collect/apply feedback, review code and
workshop logs.

Based on a patch originally by Kiryl Shutsemau.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Vishal Annapurve <vannapurve@google.com>
Acked-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Hongyu Ning <hongyu.ning@linux.intel.com>
Link: https://patch.msgid.link/20260904215841.303070-3-rick.p.edgecombe@intel.com

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