doc, aarch64: Clean up aarch64 options and documentation [PR122243]

doc, aarch64: Clean up aarch64 options and documentation [PR122243]

gcc/ChangeLog
	PR other/122243
	* config/aarch64/aarch64.opt (Wexperimental-fmv-target): Mark
	as "Undocumented".
	* doc/invoke.texi (Option Summary) <AArch64 Options>: Don't
	list "Undocumented" aarch64 options -mverbose-cost-dump or
	-Wexperimental-fmv-target, or both positive and negative forms
	of other options.  Add missing options.  Fix whitespace problems.
	(AArch64 Options): Light copy-editing.  Add missing @opindex
	entries	to match the documented options.  Undocument
	-mverbose-cost-dump and -Wexperimental-fmv-target.