iio:light:tsl2563: Add DT support

Add Device Tree support for the TSL2563 driver,
document the binding and add AMS-TAOS Inc. to the
list of vendor prefixes.

Signed-off-by: Sebastian Reichel <sre@debian.org>
Acked-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>