Read PCI_EXT_CAP_ID_DSN to query security status.

The driver will throw a warning message when a non-secure type controller
is detected. The purpose of this interface is to avoid interacting with any
firmware which is not secured/signed by Broadcom.  Any tampering on
firmware component will be detected by hardware and it will be communicated
to the driver to avoid any further interaction with that component.

Link: https://lore.kernel.org/r/20210520152545.2710479-23-kashyap.desai@broadcom.com
Cc: sathya.prakash@broadcom.com
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>