drm/i915/dp: Set relevant Downspread Ctrl DPCD bits for PR + Auxless ALPM

If a Panel Replay capable sink, supports Async Video timing in
PR active state, then source does not necessarily need to send AS SDPs
during PR active.

However, if asynchronous video timing is not supported, then for PR with
Aux-less ALPM, the source must transmit Adaptive-Sync SDPs for video
timing synchronization while PR is active.

If the source needs to send AS SDP during PR active, this requires setting
DPCD 0x0107[6] (FIXED_VTOTAL_AS_SDP_EN_IN_PR_ACTIVE). This applies whether
VRR is enabled (AVT/FAVT) or fixed-timing mode is used.

This bit defines AS SDP timing behavior during PR Active, even if AS SDPs
are briefly suspended.

Program the relevant Downspread Ctrl DPCD bits accordingly.

v2: Instead of Panel Replay check simply use AS SDP enable check. (Ville)
v3: Since the bit is defined in context of Panel Replay and AS SDP, add
    a check for both. (Ville)
v4: Extract pr_with_as_sdp logic into helper function. (Ville)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260527041050.601735-8-ankit.k.nautiyal@intel.com

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