gas: improve --gsframe documentation

I omitted documentation in 8aad677a12 in
error. Rectify that with:
1) changing ---help to mention bare `--gsframe` too, as we're not
   getting rid of that;

2) adding the new --gsframe=[no|yes] form to as.texi.

	PR gas/33125
	* gas/as.c (parse_args): Tweak --gsframe= help text.
	* gas/doc/as.texi: Document --gsframe=[no|yes].

(cherry picked from commit 50c1c57426)

gas/as.c

@@ -311,7 +311,7 @@ Options:\n\
   fprintf (stream, _("\
                           generate GNU Build notes if none are present in the input\n"));
   fprintf (stream, _("\
-  --gsframe=[no|yes]      whether to generate SFrame stack trace information\n\
+  --gsframe[={no|yes}]    whether to generate SFrame stack trace information\n\
                           (default: no)\n"));
 # if defined (TARGET_USE_SCFI) && defined (TARGET_USE_GINSN)
   fprintf (stream, _("\

gas/doc/as.texi

@@ -240,7 +240,7 @@ gcc(1), ld(1), and the Info entries for @file{binutils} and @file{ld}.
  [@b{--gdwarf-<N>}] [@b{--gdwarf-sections}]
  [@b{--gdwarf-cie-version}=@var{VERSION}]
  [@b{--generate-missing-build-notes=[no|yes]}]
- [@b{--gsframe}]
+ [@b{--gsframe}] [@b{--gsframe=[no|yes]}]
  [@b{--hash-size}=@var{N}]
  [@b{--help}] [@b{--target-help}]
  [@b{--info}] [@b{--no-info}]
@@ -860,7 +860,11 @@ configure option.
 
 @item --gsframe
 @itemx --gsframe
-Create @var{.sframe} section from CFI directives.
+@itemx --gsframe=no
+@itemx --gsframe=yes
+Create @var{.sframe} section from CFI directives.  The explicit
+@option{--gsframe=yes} option behaves the same as @option{--gsframe}.
+Generation can be suppressed with @option{--gsframe=no}.
 
 @end ifset