[Linux] update get_system_firmware.yml to get system firmware for FreeBSD

[keirazhang]

FreeBSD doesn't have /sys/firmware/efi, but can check efirt is loaded if system firmware is EFI. So, this fix is to set guest_firmware for FreeBSD.

Test passed:

+----------------------------------------------------------+
| GuestInfo Detailed Data   | architecture='X86'           |
|                           | bitness='64'                 |
|                           | distroName='FreeBSD'         |
|                           | familyName='FreeBSD'         |
|                           | kernelVersion='13.3-RELEASE' |
+----------------------------------------------------------+


Test Results (Total: 1, Passed: 1, Elapsed Time: 00:01:10)
+----------------------------------------------+
| ID | Name               | Status | Exec Time |
+----------------------------------------------+
|  1 | check_efi_firmware | Passed | 00:00:52  |
+----------------------------------------------+

[Tomorrow9]

LGTM, thanks!