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/arch/x86/cpu/u-boot-64.lds b/arch/x86/cpu/u-boot-64.lds
index ee0812a..92a30c2 100644
--- a/arch/x86/cpu/u-boot-64.lds
+++ b/arch/x86/cpu/u-boot-64.lds
@@ -15,7 +15,9 @@
 	/DISCARD/ : { *(.u_boot_list_2_cmd_*) }
 #endif
 
+#ifdef CONFIG_SYS_TEXT_BASE
 	. = CONFIG_SYS_TEXT_BASE;	/* Location of bootcode in flash */
+#endif
 	__text_start = .;
 
 	.text.start : { *(.text.start); }