i40e: Split and refactor i40e_nvm_version_str()

The function formats NVM version string according adapter's
EETrackID value. If this value OEM specific (0xffffffff) then
the reported version is with format:
"<gen>.<snap>.<release>"
and in other case
"<nvm_maj>.<nvm_min> <eetrackid> <cvid_maj>.<cvid_bld>.<cvid_min>"

These versions are reported in the subsequent patch in this series
that implements devlink .info_get but separately.

So split the function into separate ones, refactor it to use them
and remove ugly static string buffer.
Additionally convert NVM/OEM version mask macros to use GENMASK and
use FIELD_GET/FIELD_PREP for them in i40e_nvm_version_str() and
i40e_get_oem_version(). This makes code more readable and allows
us to remove related shift macros.

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