usb: phy: make PHY driver selection possible by controller drivers

Convert PHY Drivers from menuconfig to menu so that the PHY drivers
can be explicitely selected by the controller drivers.

USB_PHY is no longer a user visible option. It is upto to the PHY
drivers to select it if needed. This patch does so for the existing
PHY drivers that use the USB_PHY library.

Doing so moves the USB_PHY and PHY driver selection problem from the
end user to the PHY and controller driver developer.

e.g.

Earlier, a controller driver (e.g. EHCI_OMAP) that needs to select
a PHY driver (e.g. NOP_PHY) couldn't do so because the PHY driver
depended on USB_PHY. Making the controller driver depend on USB_PHY
has a negative effect i.e. it becomes invisible to the user till
USB_PHY is enabled. Most end users will not familiar with this.

With this patch, the end user just needs to select the controller driver
needed for his/her platform without worrying about which PHY driver to
select.

Also update USB_EHCI_MSM, USB_LPC32XX and USB_OMAP to not depend
on USB_PHY any more. They can safely select the necessary PHY drivers.

[ balbi@ti.com : refreshed on top of my next branch. Changed bool
	followed by default n into def_bool n ]

CC: Pavankumar Kondeti <pkondeti@codeaurora.org>
Acked-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>