arm64: dts: renesas: beacon: Better describe keys

The keys on the baseboard are laid out in an diamond pattern, up, down,
left, right and center.  Update the descriptions to make it easier to
read.

Signed-off-by: Adam Ford <aford173@gmail.com>
Link: https://lore.kernel.org/r/20201224170502.2254683-4-aford173@gmail.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>