[sw, dif_uart] DIF_HW_USAGE_REVIEWED complete
[sw, dif_uart] DIF_HW_USAGE_REVIEWED complete

As part of the DIF S2 signoff, we ensure that the peripheral is being
used correctly by the DIF. This review happened with Eunchan Kim,
Silvestrs Timofejevs, Sam Elliott and Garret Kelly.

Signed-off-by: Silvestrs Timofejevs <5a6466a3751cccdb6ee413d1e87698ed8baaba81@lowrisc.org>

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