Display driver shall read DPCD 00071h[3:1] during configuration
to get PSR setup time. This register provides the setup time
requirement on the VSC SDP entry packet. If setup time cannot be
met with the current timings
(e.g., PSR setup time + other blanking requirements > blanking time),
driver should enable sending VSC SDP one frame earlier before sending
the capture frame.

BSpec: 69895 (PSR Entry Setup Frames 17:16)

v2: Write frames before su entry to correct register (Ville, Jouni)
    Move frames before su entry calculation to it's
    own function (Ville, Jouni)
    Rename PSR Entry Setup Frames register to indicate
    Lunarlake specificity (Jouni)
v3: Modify setup entry frames calculation function to
    return the actual frames (Ville)
    Match comment with actual implementation (Jouni)
v4: Drop "set" from function naming (Jouni, Ville)
    Use i915 instead of dev_priv (Jouni)
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231106114228.146574-1-mika.kahola@intel.com