Promote SME2.1 and SVE2.1 ACLE status from Alpha to Beta

The SME2.1 and SVE2.1 ACLE have been implemented in upstream GCC and Clang/LLVM,
so I think they're ready to be treated as Beta.

main/acle.md

@@ -423,6 +423,8 @@ Armv8.4-A [[ARMARMv84]](#ARMARMv84). Support is added for the Dot Product intrin
 * Fixed range of operand `o0` (too small) in AArch64 system register designations.
 * Fixed SVE2.1 quadword gather load/scatter store intrinsics.
 * Removed unnecessary Zd argument from `svcvtnb_mf8[_f32_x2]_fpm`.
+* Changed the status of the SME2p1 ACLE from Alpha to Beta.
+* Changed the status of the SVE2p1 ACLE from Alpha to Beta.
 
 ### References
 
@@ -1938,7 +1940,7 @@ intrinsics are available. This implies that the following macros are nonzero:
 #### Scalable Matrix Extension (SME)
 
 The specification for SME2.1 is in
-[**Alpha** state](#current-status-and-anticipated-changes) and the
+[**Beta** state](#current-status-and-anticipated-changes) and the
 specification for the rest of SME is in
 [**Beta** state](#current-status-and-anticipated-changes).  The
 specifications may change or be extended in the future.
@@ -2016,7 +2018,7 @@ defined to a nonzero value.
 #### Half-precision floating-point SME intrinsics
 
 The specification for SME2.1 is in
-[**Alpha** state](#current-status-and-anticipated-changes) and may change or be
+[**Beta** state](#current-status-and-anticipated-changes) and may change or be
 extended in the future.
 
 `__ARM_FEATURE_SME_F16F16` is defined to `1` if there is hardware support
@@ -9083,7 +9085,7 @@ BFloat16 floating-point multiply vectors.
 ### SVE2.1 instruction intrinsics
 
 The specification for SVE2.1 is in
-[**Alpha** state](#current-status-and-anticipated-changes) and may change or be
+[**Beta** state](#current-status-and-anticipated-changes) and may change or be
 extended in the future.
 
 The functions in this section are defined by the header file
@@ -12324,7 +12326,7 @@ element types.
 ### SME2.1 instruction intrinsics
 
 The specification for SME2.1 is in
-[**Alpha** state](#current-status-and-anticipated-changes) and might change or
+[**Beta** state](#current-status-and-anticipated-changes) and might change or
 be extended in the future.
 
 The intrinsics in this section are defined by the header file
@@ -12481,7 +12483,7 @@ are named after. All of the functions have external linkage.
 ### SVE2.1 and SME2 instruction intrinsics
 
 The specification for SVE2.1 is in
-[**Alpha** state](#current-status-and-anticipated-changes) and may change or be
+[**Beta** state](#current-status-and-anticipated-changes) and may change or be
 extended in the future.
 
 The functions in this section are defined by either the header file