x86/efi: Consolidate region mapping logic

x86/efi: Consolidate region mapping logic

EFI regions are currently mapped in two separate places. The bulk of
the work is done in efi_map_regions() but when CONFIG_EFI_MIXED is
enabled the additional regions that are required when operating in
mixed mode are mapping in efi_setup_page_tables().

Pull everything into efi_map_regions() and refactor the test for
which regions should be mapped into a should_map_region() function.
Generously sprinkle comments to clarify the different cases.

Acked-by: Borislav Petkov <[email protected]>
Tested-by: Dave Young <[email protected]> [kexec/kdump]
Tested-by: Ard Biesheuvel <[email protected]> [arm]
Acked-by: Ard Biesheuvel <[email protected]>
Signed-off-by: Matt Fleming <[email protected]>