Switch the bamboo board to directly creating and configuring the UIC,
rather than doing it via the old ppcuic_init() helper function.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20201212001537.24520-5-peter.maydell@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>