drm/i915/dp: Add helper to get min sdp guardband

drm/i915/dp: Add helper to get min sdp guardband

Add a helper to compute vblank time needed for transmitting specific
DisplayPort SDPs like PPS, GAMUT_METADATA, and VSC_EXT. Latency is
based on line count per packet type.

This will be used to ensure adequate guardband when features like DSC/HDR
are enabled.

v2: Correct the lines required for PPS SDP. (Jouni)

Bspec: 70151
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://lore.kernel.org/r/20251017123504.2247954-3-ankit.k.nautiyal@intel.com