py/asmxtensa: Use proper calculation for const table offset.
py/asmxtensa: Use proper calculation for const table offset.

Instead of hard-coding it to 4 bytes.  This allows for there to be other
data stored at the very start of the emitted native code.

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