* Set VHDL standard to VHDL 2008
* Replace rcon() functuion by simple array constant
* Correct loop range in addroundkey() function

* addroundkey()
* subword()
* rotword()
* rcon()

new generic in aes.vhd: ovl_enable (boolean); copy of aes_pkg.vhd to
integrate ovl functions; copy of tb_aes.vhd to integrate ovl function