iio: dma-buffer: Kconfig: Provide titles for IIO DMA Kconfig symbols

iio: dma-buffer: Kconfig: Provide titles for IIO DMA Kconfig symbols

For some embedded systems, a workflow involving external kernel modules
that implement IIO devices is more practical than working with in-tree
sources.

Kconfig symbols without any titles do not show up in menuconfig, and as
such are more difficult to configure granularly, as they need to be
selected by potentially unused/un-needed drivers.

This change adds titles to the IIO DMA Kconfig symbols to address this.

This change also updates DMAengine -> DMAEngine, which is the
correct/nitpick-y name of the framework.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20200924111758.196367-2-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>