net: sparx5: fix unmet dependencies warning

WARNING: unmet direct dependencies detected for PHY_SPARX5_SERDES
  Depends on [n]: (ARCH_SPARX5 || COMPILE_TEST [=n]) && OF [=y] && HAS_IOMEM [=y]
  Selected by [y]:
  - SPARX5_SWITCH [=y] && NETDEVICES [=y] && ETHERNET [=y] && NET_VENDOR_MICROCHIP [=y] && NET_SWITCHDEV [=y] && HAS_IOMEM [=y] && OF [=y]

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Lars Povlsen <lars.povlsen@microchip.com>
Cc: Steen Hegelund <Steen.Hegelund@microchip.com>
Cc: UNGLinuxDriver@microchip.com
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>