py/gc: Factor out a macro to trace GC mark operations.
py/gc: Factor out a macro to trace GC mark operations.

To allow easier override it for custom tracing.

kerneltask/micropython,swegener/micropython,adafruit/micropython,pfalcon/micropython,dmazzella/micropython,infinnovation/micropython,tobbad/micropython,bvernoux/micropython,henriknelson/micropython,adafruit/circuitpython,swegener/micropython,pozetroninc/micropython,trezor/micropython,selste/micropython,adafruit/circuitpython,pramasoul/micropython,kerneltask/micropython,blazewicz/micropython,swegener/micropython,trezor/micropython,pfalcon/micropython,tralamazza/micropython,dmazzella/micropython,pfalcon/micropython,trezor/micropython,tobbad/micropython,infinnovation/micropython,henriknelson/micropython,tralamazza/micropython,adafruit/micropython,pramasoul/micropython,selste/micropython,kerneltask/micropython,bvernoux/micropython,blazewicz/micropython,swegener/micropython,adafruit/circuitpython,ryannathans/micropython,MrSurly/micropython,pramasoul/micropython,kerneltask/micropython,adafruit/micropython,adafruit/circuitpython,ryannathans/micropython,MrSurly/micropython,ryannathans/micropython,bvernoux/micropython,bvernoux/micropython,henriknelson/micropython,selste/micropython,pramasoul/micropython,adafruit/circuitpython,henriknelson/micropython,selste/micropython,pramasoul/micropython,bvernoux/micropython,infinnovation/micropython,MrSurly/micropython,adafruit/micropython,ryannathans/micropython,tobbad/micropython,tobbad/micropython,tobbad/micropython,kerneltask/micropython,pozetroninc/micropython,pozetroninc/micropython,swegener/micropython,henriknelson/micropython,pozetroninc/micropython,ryannathans/micropython,dmazzella/micropython,pfalcon/micropython,adafruit/circuitpython,blazewicz/micropython,infinnovation/micropython,tralamazza/micropython,pfalcon/micropython,MrSurly/micropython,pozetroninc/micropython,adafruit/micropython,blazewicz/micropython,dmazzella/micropython,blazewicz/micropython,trezor/micropython,selste/micropython,trezor/micropython,infinnovation/micropython,tralamazza/micropython,MrSurly/micropython