auxdisplay: add support for Titanmec TM1628 7 segment display controller

This patch adds support for the Titanmec TM1628 7 segment display
controller. It's based on previous RFC work from Andreas Färber.
The RFC version placed the driver in the LED subsystem, but this was
NAK'ed by the LED maintainer. Therefore I moved the driver to
/drivers/auxdisplay what seems most reasonable to me.

Further changes to the RFC version:
- Driver can be built also w/o LED class support, for displays that
  don't have any symbols to be exposed as LED's.
- Simplified the code and rewrote a lot of it.
- Driver is now kind of a MVP, but functionality should be sufficient
  for most use cases.
- Use the existing 7 segment support in uapi/linux/map_to_7segment.h
  as suggested by Geert Uytterhoeven.

Note: There's a number of chips from other manufacturers that are
      almost identical, e.g. FD628, SM1628. Only difference I saw so
      far is that they partially support other display modes.
      TM1628: 6x12, 7x11
      SM1628C: 4x13, 5x12, 6x11, 7x10
      For typical displays on devices using these chips this
      difference shouldn't matter.

Successfully tested on a TX3 Mini TV box that has an SM1628C and a
display with 4 digits and 7 symbols.

Co-developed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>