Documentation: RISC-V: Mention the UEFI Standards

The current patch acceptance policy requires that specifications are
approved by the RISC-V foundation, but we rely on external
specifications as well.  This explicitly calls out the UEFI
specifications that we're starting to depend on.
Reviewed-by: NConor Dooley <conor.dooley@microchip.com>
Reviewed-by: NAtish Patra <atishp@rivosinc.com>
Reviewed-by: NAnup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20221207020815.16214-4-palmer@rivosinc.comSigned-off-by: NPalmer Dabbelt <palmer@rivosinc.com>

Documentation/riscv/patch-acceptance.rst

@@ -20,9 +20,11 @@ Submit Checklist Addendum
 -------------------------
 We'll only accept patches for new modules or extensions if the
 specifications for those modules or extensions are listed as being
-"Frozen" or "Ratified" by the RISC-V Foundation.  (Developers may, of
-course, maintain their own Linux kernel trees that contain code for
-any draft extensions that they wish.)
+unlikely to be incompatibly changed in the future.  For
+specifications from the RISC-V foundation this means "Frozen" or
+"Ratified", for the UEFI forum specifications this means a published
+ECR.  (Developers may, of course, maintain their own Linux kernel trees
+that contain code for any draft extensions that they wish.)
 
 Additionally, the RISC-V specification allows implementors to create
 their own custom extensions.  These custom extensions aren't required