I/O interfaces are bank wise configurable. The maximum number of I/O pins per bank is 26. The bottom row of the each GPIO Bank table displays the available number of GPIO's for each bank. After some GPIO configuration it shows 0 , which signifies all the I/O's of the particular bank is already used. If configured, I/Os exceeds I/Os available in the bank, it will give a DRC and you should use the GPIOs in other banks.
GPIO Bank voltage can be configured from IO banks.