[FMV] Add feature CSSC.

Allows function versions which make use of the Common Short Sequence
Compression instructions. Its entry is appended after MOPS to indicate
higher priority. The request was raised here:

llvm/llvm-project#131218

Author: labrinea

Diff for: main/acle.md

@@ -454,6 +454,7 @@ Armv8.4-A [[ARMARMv84]](#ARMARMv84). Support is added for the Dot Product intrin
 * Added [**Alpha**](#current-status-and-anticipated-changes) support 
   for quarter-tile outer product intrinsics.
 * Removed the priority column from the mapping tables of Function Multi Versioning.
+* Added Function Multi Versioning feature cssc.
 
 ### References
 
@@ -2905,6 +2906,7 @@ The following table lists the architectures feature mapping for AArch64.
    | `FEAT_SME_I16I64`        | sme-i16i64    | ```ID_AA64SMFR0_EL1.I16I64 == 0b1111```   |
    | `FEAT_SME2`              | sme2          | ```ID_AA64PFR1_EL1.SMEver >= 0b0001```    |
    | `FEAT_MOPS`              | mops          | ```ID_AA64ISAR2_EL1.MOPS >= 0b0001```     |
+   | `FEAT_CSSC`              | cssc          | ```ID_AA64ISAR2_EL1.CSSC >= 0b0001```     |
 
 The tables are sorted by priority, starting from features of lowest priority ending with features of highest priority.