boards: nordic: ipc node added dcache alignement

dcache-alignement needs to be defined for ipc to have
consistent memory organization on both endpoints, when
shared memory is cacheable. nrf54h20 and nrf9280 are
using cacheable shared memory.
This is applied for ipc with icmsg backend.

Signed-off-by: Lukasz Stepnicki <lukasz.stepnicki@nordicsemi.no>