gccrs: converter: Merge dispatch into one function

Floating point and integer dispatch now have almost the same behavior,
their code could therefore be merged.

gcc/rust/ChangeLog:

	* util/rust-token-converter.cc (dispatch_float_literals): Remove
	function.
	(handle_suffix): Rename old dispatch and add one LitKind
	argument.
	(dispatch_integer_literals): Remove function.
	(convert): Change call from dispatch to suffix handler.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>