efi: Create a 64-bit app

Most modern platforms use 64-bit EFI so it is useful to have a U-Boot app
that runs under that. Add a (non-functional) build for this.

Note that --whole-archive causes the gcc 9.2 linker to crash, so disable
this for now. Once this is resolved, things should work.

For now, avoid mentioning the documentation for the 64-bit app, since it
does not work.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
index 52f71c0..700dc83 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -12,6 +12,7 @@
 	depends on !EFI_STUB || !X86 || X86_64 || EFI_STUB_32BIT
 	depends on BLK
 	depends on DM_ETH || !NET
+	depends on !EFI_APP
 	default y if !ARM || SYS_CPU = armv7 || SYS_CPU = armv8
 	select LIB_UUID
 	select PARTITION_UUIDS