phylib: make local function static

The following functions are not used directly by any drivers:
    phy_attach_direct
    phy_device_create
    phy_prepare_link
    genphy_config_advert
    genphy_setup_forced
    phy_config_interrupt
    phy_clear_interrypt
    phy_sanitize_settings
    phy_enable_interrupts
    phy_disable_interrupts

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>