MAINTAINERS: Merge TTY layer and serial drivers

Greg suggested we merge TTY layer and serial driver entries to
avoid duplicates.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Acked-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20230804102042.53576-1-tony@atomide.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>