net: phy: Make driver overloading get_phy_id depend on !COMPILE_TEST

net: phy: Make driver overloading get_phy_id depend on !COMPILE_TEST

With commit 597fe041a85f ("net/phy: enable get_phy_id redefinable") we
made get_phy_id a public but weak function, so that PHY drivers that had
required non-standard ways of getting the PHY ID could be supported.
However, overloading a weak function multiple times is (rightly) a link
error. At this point, we have two PHYs which make use of this feature,
so make both of them only available when COMPILE_TEST is unset, as part
of being able to support "allyesconfig" in the future.

Signed-off-by: Tom Rini <trini@konsulko.com>