soc: qcom: ubwc: add helper to get min_acc length

soc: qcom: ubwc: add helper to get min_acc length

MDSS and GPU drivers use different approaches to get min_acc length.
Add helper function that can be used by all the drivers.

The helper reflects our current best guess, it blindly copies the
approach adopted by the MDSS drivers and it matches current values
selected by the GPU driver.

Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Acked-by: Bjorn Andersson <andersson@kernel.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Reviewed-by: Dikshita Agarwal <dikshita.agarwal@oss.qualcomm.com>
Tested-by: Wangao Wang <wangao.wang@oss.qualcomm.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260125-iris-ubwc-v4-1-1ff30644ac81@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>