omap: clock: add clkdev aliases for EHCI clocks

Add clkdev aliases for the USBHOST and USBTLL clocks on OMAP3 and
OMAP4, so that the driver can refer to the clocks using a common alias.

This will disappear when the driver is converted to use the hwmod
database, but until then this patch is needed.

Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Acked-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Tony Lindgren <tony@atomide.com>