EFI stub documentation updates

Move efi-stub.txt out of x86 directory and into common directory
in preparation for adding ARM EFI stub support.

Signed-off-by: Roy Franz <roy.franz@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b32ebf9..ec65b51 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1579,7 +1579,7 @@
           This kernel feature allows a bzImage to be loaded directly
 	  by EFI firmware without the use of a bootloader.
 
-	  See Documentation/x86/efi-stub.txt for more information.
+	  See Documentation/efi-stub.txt for more information.
 
 config SECCOMP
 	def_bool y