ARM: OMAP4: clock data: Add missing clkdm association for dpll_usb

ARM: OMAP4: clock data: Add missing clkdm association for dpll_usb

dpll_usb needs the clkdm association so the clkdm can be
turned on before a relock. All other dplls for omap4 belong
to the ALWON (always on) domain.

The association was present as part of the older data file
(clock44xx_data.c) but looks like got accidently dropped with
the common clk convertion.

More details of the patch which fixed this up in the older
data file can be dound here..
http://www.spinics.net/lists/linux-omap/msg63076.html

Adding the .clkdm_name as part of the clk_hw_omap struct also
means a new .init needs to be part of the clk_ops for dpll_usb
to initialise the clkdm.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>