net/mlx5: HWS, add definer function to get field name str

net/mlx5: HWS, add definer function to get field name str

In preparation for complex matcher support, add function for
converting definer fname to str, which will be used in following
patches.

Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Vlad Dogaru <vdogaru@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1746992290-568936-3-git-send-email-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>