net: ethernet: ti: cpsw: refactor probe to group common hw initialization

Rework probe to group common hw initialization:
- group resources request at the beginning of the probe
- move net device initialization and registration at the end of the probe
- drop cpsw_slave_init
as preparation of refactoring of common hw initialization code to
separate function.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>