nrf52_bsim: drivers/console: Refactor printk backend

Fix a very old cmake warning for the nrf52_bsim due to the
console library being empty.
The printk backend was originally provided by the board
code for simplicity, but this left the console library
empty when building for this board.
Instead refactor that code to where all printk backends are.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>