drm: panel: jdi-lt070me05000: Add prepare_upstream_first flag

The panel driver wants to send DCS commands from the prepare
hook, therefore the DSI host wants to be pre_enabled first.
Set the flag to achieve this.

https://forums.raspberrypi.com/viewtopic.php?t=354708



Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>