auxdisplay: Move arm-charlcd binding to correct folder

This is a follow up to the commit

  00846a44 ("auxdisplay: Move arm-charlcd.c to drivers/auxdisplay folder")

for Device Tree binding.

No functional change.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rob Herring <robh@kernel.org>