iio: ti_tscadc: provide datasheet_name and scan_type

This patch provides the members "datasheet_name" and scan_type. This is
the remaining part of the earlier patch where I (bigeasy) removed iio_map
because it is now supplied by the device tree. It also static names as
suggested by Jonathan.

Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>