net: dsa: Move dsa_switch_{suspend,resume} out of legacy.c

dsa_switch_suspend() and dsa_switch_resume() are functions that belong in
net/dsa/dsa.c and are not part of the legacy platform support code.

Fixes: a6a71f19 ("net: dsa: isolate legacy code")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>