drm/i915/xe2lpd: Treat cursor plane as regular plane for DDB allocation

We now start calculating relative plane data rate for cursor plane as
well, as instructed by BSpec and also treat cursor plane same way as
other planes, when doing allocation, i.e not using fixed allocation for
cursor anymore.

Bspec: 68907
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230919192128.2045154-7-lucas.demarchi@intel.com