[aes/doc] Clarify initialization sequence
[aes/doc] Clarify initialization sequence

This commit clarifies in the documentation that software has to first
provide the configuration in CTRL_SHADOWED before providing key, IV and
data. This information got accidentally lost during a rebase of
lowRISC/OpenTitan#3018.

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

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