[dv,alert_esc_agent] Fix handling of alert init

### Description

There are a number of block level test failures due to the alert init mechanism that is triggered after a reset.

The common pattern is to see a UVM_FATAL message with a message like this:

UVM_FATAL @ 16387143 ps: (alert_receiver_driver.sv:146) [uvm_test_top.env.m_alert_agent_fatal_fault.driver] Check failed (cfg.vif.receiver_cb.alert_tx.alert_p) alert_p not high, despite an item in r_alert_rsp_q

An example failure is for clkmgr_shadow_reg_errors with almost any seed.

Assigned to @rswarbrick since I saw he made some edits of this code not long ago.