boards: arm: Add initial support for nRF54H20 PDK

Add targets that allows building for the Application and Radio cores
in the nRF54H20 SoC on the nRF54H20 PDK board.

Signed-off-by: Grzegorz Swiderski <grzegorz.swiderski@nordicsemi.no>
Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>
Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>