dt-bindings: img-ascii-lcd: Document a binding for simple ASCII LCDs

Add documentation for a devicetree binding for the simple ASCII LCD
displays found on development boards such as the MIPS Boston, MIPS Malta
& MIPS SEAD3 from Imagination Technologies.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14061/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>