devlink: add version reporting to devlink info API

ethtool -i has a few fixed-size fields which can be used to report
firmware version and expansion ROM version. Unfortunately, modern
hardware has more firmware components. There is usually some
datapath microcode, management controller, PXE drivers, and a
CPLD load. Running ethtool -i on modern controllers reveals the
fact that vendors cram multiple values into firmware version field.

Here are some examples from systems I could lay my hands on quickly:

tg3:  "FFV20.2.17 bc 5720-v1.39"
i40e: "6.01 0x800034a4 1.1747.0"
nfp:  "0.0.3.5 0.25 sriov-2.1.16 nic"

Add a new devlink API to allow retrieving multiple versions, and
provide user-readable name for those versions.

While at it break down the versions into three categories:
 - fixed - this is the board/fixed component version, usually vendors
           report information like the board version in the PCI VPD,
           but it will benefit from naming and common API as well;
 - running - this is the running firmware version;
 - stored - this is firmware in the flash, after firmware update
            this value will reflect the flashed version, while the
            running version may only be updated after reboot.

v3:
 - add per-type helpers instead of using the special argument (Jiri).
RFCv2:
 - remove the nesting in attr DEVLINK_ATTR_INFO_VERSIONS (now
   versions are mixed with other info attrs)l
 - have the driver report versions from the same callback as
   other info.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>