arm64: dts: renesas: Drop superfluous pin configuration containers

As the pin configuration child nodes for EtherAVB on the Draak and Ebisu
boards contain only a single configuration, there is no need to wrap
them in additional grandchild containers.  Hence remove the superfluous
level.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200819123910.19606-1-geert+renesas@glider.be