dt-bindings: auxdisplay: adjust example indentation and use generic node names

The example DTS should be indented with two or four (preferred) spaces,
as mentioned in Writing Schema document.  While re-indenting, change the
node names to somehow generic names, as expected by Devicetree
specification.

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ralf Schlatterbeck <rsc@runtux.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>