USB: phy: msm: Register extcon callbacks in usb_add_phy()

phy framework supports registers notificaiton callbacks for extcon,
when usb_add_phy is called if callback nb for VBUS and ID are set.
Hence set vbus_nb and id_nb callbacks for registering from phy
framework. Remove extcon related code from driver as it is no more
required.

Also move get phy_reset and phy_por_reset out of get phy_reset_clk.

Change-Id: I2f0558ca89eaf309e93b09f271db529994fc8c3e
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>