[clang][aarch64] Drop experimental from  __ARM_FEATURE_SVE_BITS macro

The __ARM_FEATURE_SVE_BITS feature macro is specified in the Arm C
Language Extensions (ACLE) for SVE [1] (version 00bet5). From the spec,
where __ARM_FEATURE_SVE_BITS==N:

    When N is nonzero, indicates that the implementation is generating
    code for an N-bit SVE target and that the arm_sve_vector_bits(N)
    attribute is available.

This was defined in D83550 as __ARM_FEATURE_SVE_BITS_EXPERIMENTAL and
enabled under the -msve-vector-bits flag to simplify initial tests.
This patch drops _EXPERIMENTAL now there is support for the feature.

[1] https://developer.arm.com/documentation/100987/latest

Reviewed By: david-arm

Differential Revision: https://reviews.llvm.org/D86720
diff --git a/clang/test/CodeGen/attr-arm-sve-vector-bits-codegen.c b/clang/test/CodeGen/attr-arm-sve-vector-bits-codegen.c
index d93be54..1a6a68a 100644
--- a/clang/test/CodeGen/attr-arm-sve-vector-bits-codegen.c
+++ b/clang/test/CodeGen/attr-arm-sve-vector-bits-codegen.c
@@ -3,7 +3,7 @@
 
 #include <arm_sve.h>
 
-#define N __ARM_FEATURE_SVE_BITS_EXPERIMENTAL
+#define N __ARM_FEATURE_SVE_BITS
 
 typedef svint32_t fixed_int32_t __attribute__((arm_sve_vector_bits(N)));
 typedef svbool_t fixed_bool_t __attribute__((arm_sve_vector_bits(N)));