ARM: OMAP5/AM43xx: remove enabling USB clocks from enable_basic_clocks()

Now that we have separate function to enable USB clocks, remove
enabling USB clocks from enable_basic_clocks(). Now board_usb_init()
should take care to invoke enable_usb_clocks() for enabling
USB clocks.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>