doc/efi: add load file 2 protocol to HTML documentation

The load file 2 protocol can be used by the Linux kernel to load the initial
RAM disk. U-Boot can be configured to provide an implementation.

Add a description to the UEFI overview and document the related functions
in the API section.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/api/efi.rst b/doc/api/efi.rst
index bc59382..631c0ce 100644
--- a/doc/api/efi.rst
+++ b/doc/api/efi.rst
@@ -125,6 +125,15 @@
 .. kernel-doc:: lib/efi_loader/efi_gop.c
    :internal:
 
+Load file 2 protocol
+~~~~~~~~~~~~~~~~~~~~
+
+The load file 2 protocol can be used by the Linux kernel to load the initial
+RAM disk. U-Boot can be configured to provide an implementation.
+
+.. kernel-doc:: lib/efi_loader/efi_load_initrd.c
+   :internal:
+
 Network protocols
 ~~~~~~~~~~~~~~~~~