[FMV] Unify ls64, ls64_v and ls64_accdata.

As originally discussed in ARM-software#315 and then in ARM-software#329 we want to unify
features that the toolchains cannot support independently. In the
case of ls64 I have attempted to split the lumped feature in the
compiler (see llvm/llvm-project#101712),
but unfortunately this would break backwards compatibility:

Mapping 'ls64' to FeatureLS64_ACCDATA would enable all three of
{FeatureLS64, FeatureLS64_V, FeatureLS64_ACCDATA} but then using
'nols64' either on the command line or the assembler directive
would only disable FeatureLS64_ACCDATA without disabling the
other two. For that we would have to map 'ls64' to FeatureLS64,
but then it would not enable the other two.

As far as I am aware there are no hardware implementations out
there which implement ls64 without ls64_v or ls64_accdata, so
unifying these features in the specification should not be a
regression for feature detection. If any of this changes in
the feature we can revisit the specification.

main/acle.md

@@ -403,6 +403,7 @@ Armv8.4-A [[ARMARMv84]](#ARMARMv84). Support is added for the Dot Product intrin
 * Added `__FUNCTION_MULTI_VERSIONING_SUPPORT_LEVEL` to indicate the support
   level of the [Function Multi Versioning](#function-multi-versioning).
 * Unified Function Multi Versioning features sha1, sha2.
+* Unified Function Multi Versioning features ls64, ls64_v, ls64_accdata.
 * Added [**Alpha**](#current-status-and-anticipated-changes)
   support for SME2.1 (FEAT_SME2p1).
 * Removed requirement to add preprocessor guards for header files.
@@ -2755,9 +2756,7 @@ The following table lists the architectures feature mapping for AArch64
    | 490           | `FEAT_SSBS`              | ssbs          | ```ID_AA64PFR1_EL1.SSBS >= 0b0001```      |
    | 500           | `FEAT_SSBS2`             | ssbs2         | ```ID_AA64PFR1_EL1.SSBS >= 0b0010```      |
    | 510           | `FEAT_BTI`               | bti           | ```ID_AA64PFR1_EL1.BT >= 0b0001```        |
-   | 520           | `FEAT_LS64`              | ls64          | ```ID_AA64ISAR1_EL1.LS64 >= 0b0001```     |
-   | 530           | `FEAT_LS64_V`            | ls64_v        | ```ID_AA64ISAR1_EL1.LS64 >= 0b0010```     |
-   | 540           | `FEAT_LS64_ACCDATA`      | ls64_accdata  | ```ID_AA64ISAR1_EL1.LS64 >= 0b0011```     |
+   | 520           | `FEAT_LS64`, `FEAT_LS64_V`, <br> `FEAT_LS64_ACCDATA` | ls64 | ```ID_AA64ISAR1_EL1.LS64 >= 0b0011``` |
    | 550           | `FEAT_WFxT`              | wfxt          | ```ID_AA64ISAR2_EL1.WFxT >= 0b0010```     |
    | 560           | `FEAT_SME_F64F64`        | sme-f64f64    | ```ID_AA64SMFR0_EL1.F64F64 == 0b1```      |
    | 570           | `FEAT_SME_I16I64`        | sme-i16i64    | ```ID_AA64SMFR0_EL1.I16I64 == 0b1111```   |