ARM: dts: Unify pinctrl-single pin group nodes for omap2

We want to unify the pinctrl-single pin group nodes to use naming "pins".
Otherwise non-standad pin group names will add make dtbs checks errors
when the pinctrl-single yaml binding gets merged.

Cc: Conor Dooley <conor+dt@kernel.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>