drivers: drm: rp1-dsi: Implement more DSI options and flags

Now implementing:
- Per-command selection of LP or HS for commands (previously LP)
- EoTp transmission option (previously EoTp was always disabled)
- Non-continuous clock option (previously always continuous)
- Per-command enabling of ACK request (in command mode only)

Make a plausible (and possibly correct) attempt to measure the
longest LP command that will fit into vertical blanking lines.

DON'T set both "Burst Mode" and "Sync Events" flags together.
This is redundant in the standard IP; in this RP1 variant it
would enable Sync Pulses but may break with some video timings.

Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>