net: ethernet: ti: cpsw: re-split res only when speed is changed

Don't re-split res in the following cases:
- speed of phys is not changed
- speed of phys is changed and no rate limited channels
- speed of phys is changed and all channels are rate limited
- phy is unlinked while dev is open
- phy is linked back but speed is not changed

The maximum speed is sum of "linked" phys, thus res are split taken
in account two interfaces, both for dual emac mode and for
switch mode.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>