boards: Add DA1469x Pro DK

This adds support for DA1469x Pro DK which is an official development
kit for DA1469x SoC series provided by Renesas.

Signed-off-by: Andrzej Kaczmarek <andrzej.kaczmarek@codecoup.pl>
Signed-off-by: Ben Lauret <ben.lauret.wm@renesas.com>