drm/msm/dpu: in dpu_format replace bitmap with unsigned long field

Using bitmap for the flags results in a clumsy syntax on test_bit,
replace it with unsigned long type and simple binary ops.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/590422/
Link: https://lore.kernel.org/r/20240420-dpu-format-v2-3-9e93226cbffd@linaro.org