dt-bindings: pinctrl: Update pinctrl-single to use yaml

dt-bindings: pinctrl: Update pinctrl-single to use yaml

Update binding for yaml and remove the old related txt bindings. Note that
we are also adding the undocumented pinctrl-single,slew-rate property. And
we only use the first example from the old binding.

As we are mostly using a generic compatible across various SoCs, let's not
start adding matches for random pin group node naming. Let's standardize on
pin group node name ending in -pins with an optional instance number
suffix.

As a pin group may have additional pins added to it later on, let's always
use -pins rather than -pin for the gropu name.

Most of the dts files have been updated already for the pin group node
names with a few changes still pending.

Cc: Nishanth Menon <nm@ti.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230721082654.27036-1-tony@atomide.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>