aarch64: Add support for FEAT_SME_FA64

Add "+sme-f64" to the list of architecture extensions.  This has already
been supported in LLVM for several years.

We don't need to update the feature requirements for any opcodes,
because FEAT_SME_FA64 only enables instructions that were already
available in non-streaming mode, and the feature checks don't know what
mode an instruction will be run under.

gas/config/tc-aarch64.c

@@ -11154,6 +11154,7 @@ static const struct aarch64_option_cpu_value_table aarch64_features[] = {
   {"sve-b16mm",		AARCH64_FEATURE (SVE_B16MM), AARCH64_FEATURE (SVE)},
   {"mtetc",		AARCH64_FEATURE (MTETC), AARCH64_FEATURE (MEMTAG)},
   {"tlbid",		AARCH64_FEATURE (TLBID), AARCH64_NO_FEATURES},
+  {"sme-fa64",		AARCH64_FEATURE (SME_FA64), AARCH64_FEATURES (2, SVE2, SME)},
   {NULL,		AARCH64_NO_FEATURES, AARCH64_NO_FEATURES},
 };
 

gas/doc/c-aarch64.texi

@@ -324,6 +324,8 @@ automatically cause those extensions to be disabled.
  @tab Enable the SME2 F16F16 Extension.
 @item @code{sme-f64f64} @tab @code{sme}
  @tab Enable SME F64F64 Extension.
+@item @code{sme-fa64} @tab @code{sme}, @code{sve2}
+ @tab Enable SME F64F64 Extension.
 @item @code{sme-i16i64} @tab @code{sme}
  @tab Enable SME I16I64 Extension.
 @item @code{sme-lutv2} @tab

gas/testsuite/gas/aarch64/sme.d

@@ -1,5 +1,6 @@
 #name: SME extension
 #as: -march=armv8-a+sme
+#as: -march=armv8-a+sme-fa64
 #objdump: -dr
 
 .*:     file format .*

include/opcode/aarch64.h

@@ -288,6 +288,8 @@ enum aarch64_feature_bit {
   AARCH64_FEATURE_MTETC,
   /* TLBI Domains.  */
   AARCH64_FEATURE_TLBID,
+  /* SME_FA64.  */
+  AARCH64_FEATURE_SME_FA64,
 
   /* Virtual features.  These are used to gate instructions that are enabled
      by either of two (or more) sets of command line flags.  */