PeiCore support

[google0101-ryan]

In the PeiCore part of OVMF's initialization, on real hardware, the IDT is used to store a pointer to an instance of EFI_PEI_SERVICES. When the pointer is needed, it is dereferenced by first executing SIDT, then reading the table pointer, and then dereferencing the first entry (which is not a real IDT entry, but rather a pointer to the service table). In Ghidra, this is nearly impossible to unmangle:

  local_8 = local_10;
  InterruptDescriptorTableRegister();
  (**(code **)(**(int **)(iStack_e + -4) + 0x24))(*(int **)(iStack_e + -4),param_1);

Could support be added to transform this into a neater call, like:

InterruptDescriptorTableStore(idt);
idt->table->peiServices->PeiNotifyPpi(idt->table->peiServices, param_1)

[google0101-ryan]

On further inspection, it appears that the EFI_PEI_SERVICES pointer is actually written before the IDT table, rather than on it, so it actually gets the table pointer from IDTR, subtracts 4 (the pointer length on IA32), and the dereferences that. The code that does so is located at line 32 of MdePkg/Library/PeiServicesTablePointerLibIdt/PeiServicesTablePointer.c in the EDK II GitHub repository, copied here for convenience:

CONST EFI_PEI_SERVICES **
EFIAPI
GetPeiServicesTablePointer (
  VOID
  )
{
  CONST EFI_PEI_SERVICES  **PeiServices;
  IA32_DESCRIPTOR         Idtr;

  AsmReadIdtr (&Idtr);
  PeiServices = (CONST EFI_PEI_SERVICES **)(*(UINTN *)(Idtr.Base - sizeof (UINTN)));
  ASSERT (PeiServices != NULL);
  return PeiServices;
}