py/emitnative: Add support for archs with windowed registers.
py/emitnative: Add support for archs with windowed registers.

Such that args/return regs for the parent are different to args/return regs
for child calls.  For an architecture to use this feature it should define
the REG_PARENT_xxx macros before including py/emitnative.c.

adafruit/circuitpython,henriknelson/micropython,tobbad/micropython,pramasoul/micropython,tobbad/micropython,trezor/micropython,adafruit/circuitpython,tobbad/micropython,trezor/micropython,trezor/micropython,MrSurly/micropython,kerneltask/micropython,henriknelson/micropython,trezor/micropython,selste/micropython,bvernoux/micropython,kerneltask/micropython,henriknelson/micropython,adafruit/circuitpython,bvernoux/micropython,MrSurly/micropython,pramasoul/micropython,bvernoux/micropython,selste/micropython,pozetroninc/micropython,selste/micropython,pozetroninc/micropython,adafruit/circuitpython,adafruit/circuitpython,kerneltask/micropython,MrSurly/micropython,MrSurly/micropython,bvernoux/micropython,pramasoul/micropython,selste/micropython,pozetroninc/micropython,henriknelson/micropython,pozetroninc/micropython,henriknelson/micropython,adafruit/circuitpython,pramasoul/micropython,kerneltask/micropython,tobbad/micropython,trezor/micropython,selste/micropython,tobbad/micropython,kerneltask/micropython,pramasoul/micropython,bvernoux/micropython,MrSurly/micropython,pozetroninc/micropython