ARM: OMAP4: clock data: lock USB DPLL on boot

Some versions of the u-boot bootloader do not lock the USB DPLL and
when the USB DPLL is not locked, then it is observed that the L3INIT
power domain does not transition to retention state during kernel
suspend on OMAP4 devices. Fix this by locking the USB DPLL at 960 MHz
on kernel boot.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>