Fix regression from commit 4d43a603, where the serial and parallel
headers got removed from char.c, which broke the alias table.

Move the HAVE_CHARDEV_SERIAL/HAVE_CHARDEV_PARPORT to osdep.h instead
of being in separate headers.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>