Simply forget the Arduino program, because Arduino ist a platform that
hides the tricky hardware. And on the FPGA you only do hardware.
To implement all of the functionality from the Arduino program in a HDL
description is a very challenging task for one never has done anything
with an FPGA.
Or did you do some simple exercises already? A LED flasher? A chasing
light? Reacting on buttons?
No?
Start with the mentioned exercises. And at last control the chasing
light (speed, direction, pattern) with buttons. Always(!!!) do a
simulation prior to go on real hardware.
Yes?
You will have to split your exercise in several modules. I would do a
module handling the LCD, one doing the interface to the sensor, one that
calculates the values to be displayed, and a top-level module that
handles the data stream.