dt-bindings: display: ssd1307fb: Add initialization properties

Document new bindings for adapting ssd1307fb driver to new displays.

Signed-off-by: Marko Kohtala <marko.kohtala@okoko.fi>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: Michal Vokáč <michal.vokac@ysoft.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190618074111.9309-6-marko.kohtala@okoko.fi