arm: dts: k3-am65: Move pinctrl nodes out of U-Boot specific dtsi

Only U-Boot specifc DT properties or overrides, must be in -u-boot.dtsi.
Pinctrl nodes does not belong here. Now that pinctrl nodes are in kernel
DT, there is no reason to be keep these in -u-boot.dtsi. Move them to
proper places so that it would ease copying DT entries from kernel DT.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>