efi_loader: capsule: add memory range capsule definitions

Memory range capsule gives us a way to notify that some memory regions
should be left untouched across the next reset.
See UEFI specification, section 8.5.3.

Since how we should handle this kind of capsule is totally up to
the system, no implementation will be added in this commit.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>