[efi] Expand the range of well-known EFI GUIDs in debug messages

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[efi] Provide efi_handle_name() for debugging

Provide a function efi_handle_name() (as a generalisation of
efi_handle_devpath_text()) which tries various methods to produce a
human-readable name for an EFI handle.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[efi] Add ability to dump all openers of a given protocol on a handle

Signed-off-by: Michael Brown <mcb30@ipxe.org>