drm/dp: move intel_dp_vsc_sdp_pack() to generic helper

intel_dp_vsc_sdp_pack() can be re-used by other DRM drivers as well.
Lets move this to drm_dp_helper to achieve this.

changes in v2:
	- rebased on top of drm-tip

Acked-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240220195348.1270854-1-quic_abhinavk@quicinc.com