drm/i915: Draw a picture about video timings

drm/i915: Draw a picture about video timings

The docs are a bit lacking when it comes to describing when certain
timing related events occur in the hardware. Draw a picture which
tries to capture the most important ones.

v2: Clarify a few details (Imre)
v3: Add HSW+ HDMI scanline counter numbers

Acked-by: Imre Deak <[email protected]>
Reviewed-by: Akash Goel <[email protected]>
Signed-off-by: Ville Syrjälä <[email protected]>
Reviewed-by: "Sourab Gupta <[email protected]>"
Signed-off-by: Daniel Vetter <[email protected]>