Add test for JTAG during uC reset

[robertszczepanski]

Test for issue #523 resolved by PR #541.

The test flow description:

1. Initiate Caliptra boot flow from the testbench typical for every test suite. The test suite awaits BOOTFSM_GO register value 0 in a loop.
2. Connect to Caliptra via JTAG (OpenOCD).
3. JTAG: Write 0 to BOOTFSM_GO register to ensure uC will not leave reset state unless permitted.
4. Caliptra SW: Initiate Firmware Update Reset which puts uC in Boot FSM wait state due to BOOTFSM_GO set to 0.
5. JTAG: Read dmstatus register until uC is in reset state.
6. JTAG: Write 1 to BOOTFSM_GO register to proceed with boot flow.
7. Caliptra SW: If reset was successful, write 1 to the mailbox to indicate successful boot.
8. JTAG: Read the mailbox until it contains 1 and finish the test.

This test has been confirmed to fail before a1a2d69.