MFC: r190117

• Set MIIF_NOLOOP and don't add IFM_LOOP as loopback apparently isn't supported with these pseudo-PHYs. The MIIF_NOLOOP flag currently triggers nothing but hopefully will be respected by mii_phy_setmedia() later on.
• Don't add IFM_NONE as isolation isn't supported by these pseudo-PHYs.
• Use mii_phy_add_media() instead of mii_add_media() so the latter can be eventually retired.