Documentation/x86: Update IOMMU spec references to use stable identifiers

Direct URLs to vendor specifications for Intel VT-d and AMD IOMMU
are frequently changed by vendors, leading to broken links in the
documentation.

Replace the fragile URLs with persistent identifiers, providing the
official document titles and IDs. This ensures users can locate the
relevant specifications regardless of vendor website restructuring.

Signed-off-by: Richard Lyu <richard.lyu@suse.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://patch.msgid.link/20260106052815.46114-1-richard.lyu@suse.com

Author: r1chard-lyu

Documentation/arch/x86/iommu.rst

@@ -2,10 +2,11 @@
 x86 IOMMU Support
 =================
 
-The architecture specs can be obtained from the below locations.
+The architecture specs can be obtained from the vendor websites.
+Search for the following documents to obtain the latest versions:
 
-- Intel: http://www.intel.com/content/dam/www/public/us/en/documents/product-specifications/vt-directed-io-spec.pdf
-- AMD: https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/specifications/48882_3_07_PUB.pdf
+- Intel: Intel Virtualization Technology for Directed I/O Architecture Specification (ID: D51397)
+- AMD: AMD I/O Virtualization Technology (IOMMU) Specification (ID: 48882)
 
 This guide gives a quick cheat sheet for some basic understanding.