Ssu64xl is mandatory in RVA22S64

RVA22S64 is ratified and so should not be changed, but I claim this is not
a semantic change.  It isn't possible to implement RVA22U64 and RVA22S64
together without having implemented the Ssu64xl extension along the way.
The reasoning is as follows.  When SXLEN=64 (as is the case for RVA22S64),
the PrivArch v1.12 spec requires the sstatus.UXL field exist and be encoded
the same as MXL.  The table in the M-mode chapter that describes MXL's encoding
only lists 3 values (RV32=1, RV64=2, RV128=3); it does not provide for
representing XLEN=64 with any value other than 2.  Since RVA22U64 requires
UXLEN=64, it follows that sstatus.UXL must be capable of holding the value 2,
which is exactly what Ssu64xl stipulates.

profiles.adoc

@@ -900,10 +900,16 @@ NOTE: This is new extension name capturing this feature.
 
 - *Svinval* Fine-Grained Address-Translation Cache Invalidation
 
+- *Ssu64xl* `sstatus.UXL` must be capable of holding the value 2
+(i.e., UXLEN=64 must be supported).
+
+NOTE: This is a new extension name for this feature.
+
+
 ==== RVA22S64 Optional Extensions
 
 RVA22S64 has four unprivileged options (Zfh, V, Zkn, Zks) from
-RVA22U64, and eight privileged options (Sv48, Sv57, Svnapot, Ssu64xl,
+RVA22U64, and eight privileged options (Sv48, Sv57, Svnapot,
 Sstc, Sscofpmf, Zkr, H).
 
 The privileged optional extensions are:
@@ -917,11 +923,6 @@ The privileged optional extensions are:
 NOTE: It is expected that Svnapot will be mandatory in the next
 profile release.
 
-- *Ssu64xl* `sstatus.UXL` must be capable of holding the value 2
-(i.e., UXLEN=64 must be supported).
-
-NOTE: This is a new extension name for this feature.
-
 - *Sstc* supervisor-mode timer interrupts.
 
 NOTE: Sstc was not made mandatory in RVA22S64 as it is a more