cpu: mips_pic32_common: Refactor UART
cpu: mips_pic32_common: Refactor UART

Signed-off-by: Francois Berder <880c5b95aa239388d35adb184ba52ce6e74e78eb@users.noreply.github.com>

yogo1212/RIOT,OTAkeys/RIOT,authmillenon/RIOT,basilfx/RIOT,kYc0o/RIOT,authmillenon/RIOT,kYc0o/RIOT,miri64/RIOT,ant9000/RIOT,ant9000/RIOT,kYc0o/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,miri64/RIOT,kaspar030/RIOT,OTAkeys/RIOT,basilfx/RIOT,yogo1212/RIOT,OTAkeys/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,ant9000/RIOT,kaspar030/RIOT,yogo1212/RIOT,miri64/RIOT,kYc0o/RIOT,authmillenon/RIOT,ant9000/RIOT,basilfx/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,basilfx/RIOT,OlegHahm/RIOT,authmillenon/RIOT,yogo1212/RIOT,OlegHahm/RIOT,jasonatran/RIOT,yogo1212/RIOT,OlegHahm/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,ant9000/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,kYc0o/RIOT,jasonatran/RIOT,miri64/RIOT,jasonatran/RIOT,authmillenon/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,miri64/RIOT,basilfx/RIOT,kaspar030/RIOT