docs: move x86 documentation into Documentation/arch/

Move the x86 documentation under Documentation/arch/ as a way of cleaning
up the top-level directory and making the structure of our docs more
closely match the structure of the source directories it describes.

All in-kernel references to the old paths have been updated.

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20230315211523.108836-1-corbet@lwn.net/
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index bdfe08f..c5d614d 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -97,7 +97,7 @@
 	  code. When you use it make sure you have a big enough
 	  IOMMU/AGP aperture.  Most of the options enabled by this can
 	  be set more finegrained using the iommu= command line
-	  options. See Documentation/x86/x86_64/boot-options.rst for more
+	  options. See Documentation/arch/x86/x86_64/boot-options.rst for more
 	  details.
 
 config IOMMU_LEAK