firmware_uefi: EfiDiagnostics flush on inspect_mut

[maheeraeron]

This PR focuses on allowing EfiDiagnostics to force flush through InspectMut.

We will only print EfiDiagnostics to our tracing facilities ONLY IF WE WRITE to the inspect_diagnostics field to true in UefiDevice.

To trigger this, use inspect like so:

openvmm> inspect -u true vm/uefi/process_diagnostics

[maheeraeron]

Current state of inspect usage:

openvmm> inspect vm/uefi
{
    address: 0x30,
    command_set: "x64",
    dependencies: "vmtime,lines/gpe0",
    dependents: "chipset",
    process_diagnostics: "Use: inspect -u 1 vm/uefi/process_diagnostics",
    service: _,
    unit_state: "running",
    use_mmio: false,
}

openvmm> inspect vm/uefi/process_diagnostics
"Use: inspect -u 1 vm/uefi/process_diagnostics"

openvmm> inspect -u 1 vm/uefi/process_diagnostics
  74.517116809s  INFO firmware_uefi::service::diagnostics:  EFI log entry debug_level=LOAD+ERROR ticks=0xea9fa phase=PEI_CORE log_message="PcdPeim.efi"
  74.517258083s  INFO firmware_uefi::service::diagnostics:  EFI log entry debug_level=LOAD+ERROR ticks=0xead4e phase=PEI_CORE log_message="ResetSystemPei.efi"
 [...more UEFI logs...]
  74.522973465s  INFO firmware_uefi::service::diagnostics:  processed EFI log entries triggered_by="inspect" entries_processed=0x67 bytes_read=0x1f88
"attempted to process diagnostics"

This last case is weird... did I do something wrong? I wonder if this is because -u recursively applies to child nodes too?

openvmm> inspect -u 1 vm/uefi
  80.758912712s  INFO firmware_uefi::service::diagnostics:  EFI log entry debug_level=LOAD+ERROR ticks=0xea9fa phase=PEI_CORE log_message="PcdPeim.efi"
  80.758997101s  INFO firmware_uefi::service::diagnostics:  EFI log entry debug_level=LOAD+ERROR ticks=0xead4e phase=PEI_CORE log_message="ResetSystemPei.efi"
 [...more UEFI logs...]
  80.765001391s  INFO firmware_uefi::service::diagnostics:  processed EFI log entries triggered_by="inspect" entries_processed=0x67 bytes_read=0x1f88
error: unresolved