Extend SERIAL_CHAR to take multiple arguments

Marlin/src/HAL/HAL_AVR/pinsDebug.h

Marlin/src/HAL/shared/backtrace/backtrace.cpp

Marlin/src/core/serial.h

Marlin/src/core/utility.cpp

Marlin/src/feature/bedlevel/bedlevel.cpp

Marlin/src/feature/runout.h

Marlin/src/gcode/calibrate/M100.cpp

Marlin/src/gcode/calibrate/M425.cpp

Marlin/src/gcode/config/M221.cpp

Marlin/src/gcode/host/M114.cpp

Marlin/src/gcode/parser.cpp

Marlin/src/libs/L6470/L6470_Marlin.cpp

Marlin/src/module/endstops.cpp

Marlin/src/module/stepper.cpp