Add CONSOLE=1 compile flag to assign TX/RX pins to zephyr console #11597

• Addressed as part of zephyr-cp: dynamic buses on the Feather nRF52840 boards #11576.

In zephyr nordic and maybe other boards, the TX/RX pins were assigned to the Zephyr console in the devicetree. Turn off that assignment by default, and put it back if a build is done with CONSOLE=1.

The Zephyr console is used for printk(), log messages, fatal errors, etc. If the Zephyr shell were turned on, it would also be used for that.