efi_loader: implement EFI_DEVICE_PATH_TO_TEXT_PROTOCOL

ConvertPathToText is implemented for
* type 4    - media device path
* subtype 4 - file path

This is the kind of device path we hand out for block devices.

All other cases may be implemented later.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
[agraf: fix whitespace]
Signed-off-by: Alexander Graf <agraf@suse.de>

cmd/bootefi.c

@@ -84,6 +84,10 @@ static struct efi_object loaded_image_info_obj = {
 			.guid = &efi_guid_console_control,
 			.protocol_interface = (void *) &efi_console_control
 		},
+		{
+			.guid = &efi_guid_device_path_to_text_protocol,
+			.protocol_interface = (void *) &efi_device_path_to_text
+		},
 	},
 };