doc: integrate UEFI documentation into Sphinx toctree

Change the UEFI documentation to Sphinx style and integrate it into the
rest of the Sphinx generated documentation.

Remove the inaccurate TODO list in doc/uefi/uefi.rst.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index c28251e..182c9c7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -485,9 +485,7 @@
 R:	Alexander Graf <agraf@csgraf.de>
 S:	Maintained
 T:	git https://gitlab.denx.de/u-boot/custodians/u-boot-efi.git
-F:	doc/README.uefi
-F:	doc/README.iscsi
-F:	doc/efi.rst
+F:	doc/uefi/*
 F:	include/capitalization.h
 F:	include/charset.h
 F:	include/cp1250.h