drm/i915/dsb: Introduce intel_dsb_wait_vblank_delay()

Add intel_dsb_wait_vblank_delay() which instructs the DSB
to wait for duration between the undelayed and delayed vblanks.
We'll need this as the DSB can only directly wait for the
undelayed vblank, but we'll need to wait until the delayed
vblank has elapsed as well.

Reviewed-by: Animesh Manna <animesh.manna@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240930170415.23841-10-ville.syrjala@linux.intel.com