drm/msm/dpu: remove duplicate code calculating sum of bandwidths

The code in dpu_core_perf_crtc_check() mostly duplicates code in
dpu_core_perf_aggregate(). Remove the duplication by reusing the latter
function.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/636059/
Link: https://lore.kernel.org/r/20250209-dpu-perf-rework-v5-2-87e936cf3004@linaro.org