auxdisplay: linedisp: Add missing header(s)

Do not imply that some of the generic headers may be always included.
Instead, include explicitly what we are direct user of.

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