mlxsw: Move PCI id table definitions into driver modules

So far, mlxsw_pci.ko is the module that registers PCI table for all
drivers (spectrum and switchx2). That is problematic for example with
dracut. Since mlxsw_spectrum.ko and mlxsw_switchx2.ko are loaded
dynamically from within mlxsw_core.ko, dracut does not have track of
them and avoids them from being included in initramfs.

So make this in an ordinary way and define the PCI tables in individual
driver modules, so it can be properly loaded and included in dracut
initramfs image. As a side effect, this patch could remove no longer
necessary driver "kind" strings which were used to link PCI ids with
individual mlxsw drivers.

Suggested-by: Ivan Vecera <ivecera@redhat.com>
Tested-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>