drivers: mb_display: rework bbc:microbit display support

Rework bbc:microbit display support to use nRF LED matrix
display controller driver and allow to use it with
bbc:microbit v2 board.

This patch turns the driver into a higher level driver
using the display controller API. Code that directly
accesses hardware (GPIO) is removed.
This driver is reworked to be more generic. It still
has a lot of potential for improvement, but it requires
changes in all applications that use this tool.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>