FPGA Bank Power On-Off Separately
I've already know that the bank 1 and 8 need to be powered up with the core


Under these circumstances FPGA exits power-on-reset and starts configuring, see here page 2-26. But it is a good question if it will function properly in user mode.


  The question is, for all the other banks, bank 2 to 7, is it safe to power them up and down separately?


There were a number of questions related to shutting down I/O voltages, for example this one, there's even Altera's answer to related question for Stratix IV FPGA.

However, for MAX 10, if you would look at page 6 of the datasheet for MAX 10 family, you will see in the footer


  (2) VCCIO for all I/O banks must be powered up during user mode because VCCIO I/O banks are used for the ADC and I/O functionalities


Thus in general if you do not use I/O pins, there will be tiny power saving from powering down their respective VCCIO, however you risk to catch issue when this power is used for something else inside the chip.

The best, from my point of view, is to follow manufacturer's guidelines. Or you can file a support incident with them, but I bet they will refer you to the documentation and will not seriously spend a minute on this incident.