UPSTREAM: drm/i915/dsb: Introduce intel_dsb_wait_vblanks()

Add a function to emit a DSB wait for vblank instruction. This
just waits until the specified number of vblanks.

Note that this triggers on the transcoder's undelayed vblank,
as opposed to the pipe's delayed vblank.

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/20240930170415.23841-8-ville.syrjala@linux.intel.com


(cherry picked from commit d6dfbc6f)

Bug: 406266020
Bug: 387910155
Test: DUT booted to UI

Change-Id: Ie06ab2a75a8f40359f300f4054da97ac460d3112
Signed-off-by: George D Sworo <george.d.sworo@intel.corp-partner.google.com>
Signed-off-by: Ryan Neph <ryanneph@google.com>