Revert "drm/i915: Extract drm_dp_atomic_find_vcpi_slots cycle to separate function"

This reverts commit 7ae5ab44.

Part of a series where patches were modified while applying to resolve
conflicts, leading to further conflicts between drm-misc-next and
drm-intel-next, resulting in build failures in drm-tip. To be applied
again on a baseline with drm-misc-next and drm-intel-next in sync.

Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>