locations-functions.pl: Allow get_locations() function to skip special locations.

When adding "no_special_locations" to the function call as argument
the special locations liks "A1, A2, A3 etc" will not be added to the
returned array as available locations.

Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>