devicetree: Fix argument order for DT_*_CELL_BY_IDX

The cell paramater should have been last to match both the
DT_*_CELL_BY_NAME macros as well as how DT_PHA_BY_IDX works.  We fix the
DT_INST_*_CELL_BY_NAME macros as well.

The dma macro's implemented the behavior correctly, but got the argument
names in correct.  We fix that to make everything consistent.

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