dt-bindings: riscv: Add Svrsw60t59b extension description

Add description for the Svrsw60t59b extension (PTE Reserved for SW
bits 60:59) extension which was ratified recently in
riscv-non-isa/riscv-iommu.

Link: https://lkml.kernel.org/r/20251113072806.795029-7-zhangchunyan@iscas.ac.cn
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Jones <ajones@ventanamicro.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Conor Dooley <conor@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -217,6 +217,12 @@ properties:
             memory types as ratified in the 20191213 version of the privileged
             ISA specification.
 
+        - const: svrsw60t59b
+          description:
+            The Svrsw60t59b extension for providing two more bits[60:59] to
+            PTE/PMD entry as ratified at commit 28bde925e7a7 ("PTE Reserved
+            for SW bits 60:59") of riscv-non-isa/riscv-iommu.
+
         - const: svvptc
           description:
             The standard Svvptc supervisor-level extension for