i40e: Add handler for devlink .info_get

Provide devlink .info_get callback to allow the driver to report
detailed version information. The following info is reported:

 "serial_number" -> The PCI DSN of the adapter
 "fw.mgmt" -> The version of the firmware
 "fw.mgmt.api" -> The API version of interface exposed over the AdminQ
 "fw.psid" -> The version of the NVM image
 "fw.bundle_id" -> Unique identifier for the combined flash image
 "fw.undi" -> The combo image version

With this, 'devlink dev info' provides at least the same amount
information as is reported by ETHTOOL_GDRVINFO:

$ ethtool -i enp2s0f0 | egrep '(driver|firmware)'
driver: i40e
firmware-version: 9.30 0x8000e5f3 1.3429.0

$ devlink dev info pci/0000:02:00.0
pci/0000:02:00.0:
  driver i40e
  serial_number c0-de-b7-ff-ff-ef-ec-3c
  versions:
      running:
        fw.mgmt 9.130.73618
        fw.mgmt.api 1.15
        fw.psid 9.30
        fw.bundle_id 0x8000e5f3
        fw.undi 1.3429.0

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>