The last patch added the dependency on 'OF && HAS_IOMEM' but left
COMPILE_TEST as an alternative, which kind of defeats the purpose
of adding the dependency, we still get randconfig build warnings:

warning: (NET_DSA_BCM_SF2 && BCMGENET) selects MDIO_BCM_UNIMAC which has unmet direct dependencies (NETDEVICES && MDIO_BUS && HAS_IOMEM && OF_MDIO)

For compile-testing purposes, we don't really need this anyway,
as CONFIG_OF can be enabled on all architectures, and HAS_IOMEM
is present on all architectures we do meaningful compile-testing on
(the exception being arch/um).

This makes both OF and HAS_IOMEM hard dependencies.

Fixes: 5af74bb4 ("net: bcmgenet: Add dependency on HAS_IOMEM && OF")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>