x86: Allow booting a kernel from the EFI app

At present this is disabled, but it should work so long as the kernel does
not need EFI services. Enable it and add a note about remaining work.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/uefi/u-boot_on_efi.rst b/doc/develop/uefi/u-boot_on_efi.rst
index 8f81b79..acad639 100644
--- a/doc/develop/uefi/u-boot_on_efi.rst
+++ b/doc/develop/uefi/u-boot_on_efi.rst
@@ -269,7 +269,7 @@
 
 - Avoid turning off boot services in the stub. Instead allow U-Boot to make
   use of boot services in case it wants to. It is unclear what it might want
-  though.
+  though. It is better to use the app.
 
 Where is the code?
 ------------------