auxdisplay: Move panel.c to drivers/auxdisplay folder

It looks like panel.c belongs to auxdisplay subsystem.

Move it to drivers/auxdisplay folder.
No functional changes intended.

Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>