dts: Rename DT_.*_GPIO_* to DT_.*_GPIOS_*

Convert DT_.*_GPIO_{CONTROLLER,PIN,FLAGS} ->
	DT_.*_GPIOS_{CONTROLLER,PIN,FLAGS)

Used the following commands to make these conversions:

git grep -l DT_.*_GPIO_CONTROLLER | xargs sed -i 's/DT_\(.*\)_GPIO_CONTROLLER/DT_\1_GPIOS_CONTROLLER/g'
git grep -l DT_.*_GPIO_PIN | xargs sed -i 's/DT_\(.*\)_GPIO_PIN/DT_\1_GPIOS_PIN/g'
git grep -l DT_.*_GPIO_FLAGS | xargs sed -i 's/DT_\(.*\)_GPIO_FLAGS/DT_\1_GPIOS_FLAGS/g'

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