boards: nrf54h20dk: introduce revision 0.8.0 (current)

The current DK is labeled as revision 0.8.0. Until now, no revisions were
needed, but a new hardware spin is coming, so we'll need to keep at least
two revisions in the near future until the final one becomes the default.
Prepare the board for that scenario. Note that the "old" nRF54H20 SoC is
now nRF54H20 EngB.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>