devicetree: deprecate DT_IO_CHANNELS_LABEL APIs

Mark all variants of the DT_IO_CHANNELS_LABEL APIs:
* DT_IO_CHANNELS_LABEL_BY_IDX
* DT_IO_CHANNELS_LABEL_BY_NAME
* DT_IO_CHANNELS_LABEL
* DT_INST_IO_CHANNELS_LABEL_BY_IDX
* DT_INST_IO_CHANNELS_LABEL_BY_NAME
* DT_INST_IO_CHANNELS_LABEL

As deprecated in favor of utilizing:

* DT_IO_CHANNELS_CTLR_BY_IDX
* DT_IO_CHANNELS_CTLR_BY_NAME
* DT_IO_CHANNELS_CTLR
* DT_INST_IO_CHANNELS_CTLR_BY_IDX
* DT_INST_IO_CHANNELS_CTLR_BY_NAME
* DT_INST_IO_CHANNELS_CTLR

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>