efi/cper: Export several helpers for ghes_edac to use

Before ghes_edac can be turned back into a proper module again, export
several helpers which are going to be used by it.

Signed-off-by: Jia He <justin.he@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20221010023559.69655-2-justin.he@arm.com