drm/msm/dpu: simplify _dpu_format_populate_plane_sizes_*

drm/msm/dpu: simplify _dpu_format_populate_plane_sizes_*

Move common bits of _dpu_format_populate_plane_sizes_ubwc() and
_linear() to dpu_format_populate_plane_sizes(), reducing unnecessary
duplication and simplifying code flow fror the UBWC function.

Reviewed-by: Jessica Zhang <jessica.zhang@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/688178/
Link: https://lore.kernel.org/r/20251114-dpu-formats-v3-9-cae312379d49@oss.qualcomm.com
Tested-by: Luca Weiss <luca.weiss@fairphone.com> # qcm6490-fairphone-fp5
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>