ARM: davinci: make dm644x-evm phy fixup conditional

We cannot call phy_register_fixup_for_uid() if CONFIG_PHYLIB
is not built into the kernel, and we should not enforce that
to be built into vmlinux either, because one might want to
disable the entire network stack.

This change uses a compile-time condition on CONFIG_PHYLIB
to remove the call in the cases where it cannot work.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: davinci-linux-open-source@linux.davincidsp.com