drm/i915/psr: New interface adding PSR idle poll into dsb commit

We are currently observing crc failures after we started using dsb for PSR
updates as well. This seems to happen because PSR HW is still sending
couple of updates using old framebuffers on wake-up.

This patch is preparing to fix that by adding interface which can be used
to add poll ensuring PSR HW is idle into dsb commit.

v3: add intel_dsb as a parameter to intel_psr_wait_for_idle_dsb
v2: add pass crtc_state->dsb_commit as parameter

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20250905072708.2659411-4-jouni.hogander@intel.com