acrn-board-inspector fails when no DMAR table is present

[tklengyel]

Describe the bug
Running acrn-board-inspector in the Simics Public release fails due to no DMAR ACPI table being present.

Platform
Simics Public Release QSP-x86-CPU.

Codebase
Latest git master branch (925e3d9)

Scenario
N/A

To Reproduce
Install Ubuntu in Simics, install acrn-board-inspector, run. All according to the getting started guide.

Expected behavior
Generating the board xml.

Additional context

 10%|█         | 10/100 [00:01<00:11,  7.61it/s]Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/acrn_board_inspector/legacy/board_parser.py", line 110, in <module>
    acpi.generate_info(BOARD_INFO)
  File "/usr/lib/python3/dist-packages/acrn_board_inspector/legacy/acpi.py", line 655, in generate_info
    gen_acpi_info(config)
  File "/usr/lib/python3/dist-packages/acrn_board_inspector/legacy/acpi.py", line 625, in gen_acpi_info
    dmar.write_dmar_data(SYS_PATH[1] + 'DMAR', config)
  File "/usr/lib/python3/dist-packages/acrn_board_inspector/legacy/dmar.py", line 359, in write_dmar_data
    (dmar_tbl, dmar_hw_list, dmar_dev_list, drhd_cnt) = walk_dmar_table(
  File "/usr/lib/python3/dist-packages/acrn_board_inspector/legacy/dmar.py", line 308, in walk_dmar_table
    data = open(sysnode, 'rb').read()
FileNotFoundError: [Errno 2] No such file or directory: '/sys/firmware/acpi/tables/DMAR'
2024-02-27 23:52:18-root-CRITICAL:-Command '['/usr/bin/python3', '/usr/lib/python3/dist-packages/acrn_board_inspector/legacy/board_parser.py', 'simics_pub', '--out', 'simics_pub.xml']' returned non-zero exit status 1.
 10%|█         | 10/100 [00:01<00:15,  5.67it/s]

There really is no DMAR table there, so the board-inspector should handle this scenario gracefully.