fbdev: ssd1307fb: Unify init code and obtain hw specific bits from DT

fbdev: ssd1307fb: Unify init code and obtain hw specific bits from DT

The 130X controllers are very similar from the configuration point of view.
The configuration registers for the SSD1305/6/7 are bit identical (except the
the VHCOM register and the the default values for clock setup register). This
patch unifies the init code of the controller and adds hardware specific
properties to DT that are needed to correctly initialize the device.

The SSD130X can be wired to the OLED panel in various ways. Even for the
same controller this wiring can differ from one display module to another
and can not be probed by software. The added DT properties reflect these
hardware decisions of the display module manufacturer.
The 'com-sequential', 'com-lrremap' and 'com-invdir' values define different
possibilities for the COM signals pin configuration and readout direction
of the video memory. The 'segment-no-remap' allows the inversion of the
memory-to-pin mapping ultimately inverting the order of the controllers
output pins. The 'prechargepX' values need to be adapted according to the
capacitance of the OLEDs pixel cells.

So far these hardware specific bits are hard coded in the init code, making
the driver usable only for one certain wiring of the controller. This patch
makes the driver usable with all possible hardware setups, given a valid hw
description in DT. If these values are not set in DT the default values,
as they are set in the ssd1307 init code right now, are used. This implies
that without the corresponding DT property "segment-no-remap" the segment
remap of the ssd130X controller gets activated. Even though this is not the
default behaviour according to the datasheet it maintains backward
compatibility with older DTBs.

Note that the SSD1306 does not seem to be using the configuration written to
the registers at all. Therefore this patch does not try to maintain these
values without changes in DT. For reference an example is added to the DT
bindings documentation that reproduces the configuration that is set in the
current init code.

Signed-off-by: Thomas Niederprüm <niederp@physik.uni-kl.de>
Tested-by: Olliver Schinagl <o.schinagl@ultimaker.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>