dt-bindings: net: mdio: Drop resets/reset-names child properties

resets/reset-names are device specific and don't belong in the MDIO bus
schema. For example, it doesn't match what is defined for the
"qca,ar9331-switch" binding which defines "reset-names" to be "switch"
rather than "phy". Neither name is that useful IMO.

Other child properties are also device specific, but those won't conflict
with device schemas.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220111170248.3160841-1-robh@kernel.org