The "vanilla" Alpha PLL configs are sometimes provided with an intention
to only update certain bits of th register.

Do so if a mask is found.
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Iskren Chernev <me@iskren.info>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230601-topic-alpha_ctl-v1-1-b6a932dfcf68@linaro.org