net/mlx5: E-Switch, Refactor vport representors initialization

Refactor the init stage of vport representors registration.
vport number and hw id can be assigned by the E-Switch driver and not by
the netdevice driver. While here, make the error path of mlx5_eswitch_init()
a reverse order of the good path, also use kcalloc to allocate an array
instead of kzalloc.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>