drm/i915/dsb: Allow DSB based commits when scalers are in use

drm/i915/dsb: Allow DSB based commits when scalers are in use

Have DSB perform plane scaler programming as well. Changes
to pfit/pipe scaler are not being done on the dsb since those
take the fastset path. However we do now allow DSB based plane
updates when the pfit/pipe scaler is currently enabled (the
pfit/pipe scaler just won't be touched by the DSB).

Fortunately the hardware issue where some scaler registers
are latched at frame start and some at start of vblank has
been fixed on icl+ (IIRC), and since DSB is tgl+ only we
don't have to do any changes to the DSB vblank evasion.
Not that we handle that hardware issue correctly in the
CPU vblank evasion either...

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250218205850.1422-4-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shakar@intel.com>