Fix PCB legend print

[db8fs]

The Eagle PCB supports two board variants: RPi-host usage (directly on top of RaspberryPi) and the usage as daisy-chained client.

Some features are not available on client usage, they therefore don't need component placing and may lead to wrong assumption of the board behavior. For instance, the +5V supply isn't available on slave boards, also the PWM and SPI-features aren't there.

This should be clearly visible on PCB legend print.