drm/lease: debug output for lease creation

I spent a bit of time scratching heads and figuring out why the igts
don't work. Probably useful to keep this work.

Cc: Keith Packard <keithp@keithp.com>
Cc: Dave Airlie <airlied@gmail.com>
Acked-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181102132543.16486-1-daniel.vetter@ffwll.ch