[aes] Reduce bit width of sparsely encoded mux2 selector signal type
[aes] Reduce bit width of sparsely encoded mux2 selector signal type

This type is used for many control signals and we can save one additional
bit without sacrificing security.

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

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