phy: rename struct omap_control_usb to struct omap_control_phy

Rename struct omap_control_usb to struct omap_control_phy since it can
be used to control PHY of USB, SATA and PCIE. Also move the driver and
include files under *phy* and made the corresponding changes in the users
of phy-omap-control.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>