stm32/adc: Increase sample time for internal sensors on L4 MCUs.
stm32/adc: Increase sample time for internal sensors on L4 MCUs.

They need time (around 4us for VREFINT) to obtain accurate results.

Fixes issue #4022.

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