auxdisplay: make PANEL a menuconfig

This change makes xconfig present the PANEL drivers immediately
following the AUXDISPLAY drivers instead of under the major menu
item "Device Drivers". It also unclutters the Device Drivers menu in
nconfig and menuconfig by moving the PANEL drivers to a sub-menu.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>