usb: ehci: omap: add support for TLL mode on OMAP4

The EHCI controller in OMAP4 supports a transceiver-less link
mode (TLL mode), similar to the one in OMAP3. On the OMAP4
however, there are an additional set of clocks that need
to be turned on to get this working.

Request and configure these for each port if that port
is connected in TLL mode.

Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>