Bluetooth: drivers: Update to use new H:4 buffer encoding

Update all HCI drivers to use the new H:4 encoding for buffers passing
to/from drivers.

One behavioral change that's done in favor of simplicity, is that where
there's previously been switch statements that could return an error for
unsupported packet types now simply pass any received packet unchanged to
lower layers of the controller (or the HCI transport). Handling this is
now the responsibility of the lower layers, however in practice hitting
such scenarios means that there's a mismatch between configured host and
controller features.

Signed-off-by: Johan Hedberg <johan.hedberg@silabs.com>