efi_loader: rename struct efi_initrd_dp to efi_lo_dp_prefix

As we now also store device-tree device-paths in load options rename
struct efi_initrd_dp to efi_lo_dp_prefix.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/include/efi_load_initrd.h b/include/efi_load_initrd.h
index be5d5a7..9feafb1 100644
--- a/include/efi_load_initrd.h
+++ b/include/efi_load_initrd.h
@@ -18,7 +18,17 @@
 		 0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68)
 extern const efi_guid_t efi_lf2_initrd_guid;
 
-struct efi_initrd_dp {
+/**
+ * struct efi_lo_dp_prefix - separator device path used in load options
+ *
+ * We use vendor media device nodes in UEFI load options to separate
+ * the binary, initrd, and fdt device-paths. This structure contains
+ * the vendor media device node and an end node.
+ *
+ * @vendor:	vendor media device node
+ * @end:	end node
+ */
+struct efi_lo_dp_prefix {
 	struct efi_device_path_vendor vendor;
 	struct efi_device_path end;
 } __packed;