phy: Add empty generic_phy_configure() implementation for PHY disabled case

In case PHY is not enabled, the generic_phy_configure() implementation is
missing. Add an empty one so that the list of empty functions is complete.

Fixes: f8da8a82 ("generic-phy: add configure op")
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>