[sram/dv] Fix regwen test failures
[sram/dv] Fix regwen test failures

Used `ctrl_regwen` mirrored value to gate key_req and init operations

Signed-off-by: Weicai Yang <4fa8c7762ee4da95e3dee7dae2c3263ea16637f9@google.com>

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