auxdisplay: Add 7 and 14 segment mappings to MAINTAINERS

The mapping files are tightly related to auxdisplay subsystem.
Add them to the MAINTAINERS database.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>