[aes] Replace '{default:} by loop statements for parameterized signals
[aes] Replace '{default:} by loop statements for parameterized signals

This is needed for Synopsys Design Compiler.

Signed-off-by: Pirmin Vogel <386a7fc8e7338ed7899b4d9883c0ebec5de81366@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan