Enable the SPI bus to configure the display and program its ram. For
that the fastest available SPI clock is used. To configure the display
a minimal config is used which is not identical but similar to the
displays datasheet. The display can only be filled columnwise so far.
Generate a variable duty cycle PWM signal for the dimmable display
backlight at a frequency of 1.25kHz.
For demo und testing purposes PD5 is currently fading between 0 and
100%.
