efi_loader: document functions in efi_rng.c

Add the missing Sphinx documentation.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/api/efi.rst b/doc/api/efi.rst
index 2ca3449..bc59382 100644
--- a/doc/api/efi.rst
+++ b/doc/api/efi.rst
@@ -131,6 +131,12 @@
 .. kernel-doc:: lib/efi_loader/efi_net.c
    :internal:
 
+Random number generator protocol
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: lib/efi_loader/efi_rng.c
+   :internal:
+
 Text IO protocols
 ~~~~~~~~~~~~~~~~~