how to check the NIOSII code footprint size

Depends to some extent on what you are tryign to find out.

The actual sizes of the code/data sections can be found by running 'objdump' on the object and program files.

The symbol table will give some idea as to the size of each function, and the included functions.

If you want to know why some functions are included from a library (eg libc) the linker map file will tell you (if generated, and with appropriate linker options).