bcm281xx: add support for "USB OTG clock"

enable this clock with the following:
  clk_usb_otg_enable((void *)HSOTG_BASE_ADDR)

Signed-off-by: Steve Rae <srae@broadcom.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
diff --git a/arch/arm/cpu/armv7/bcm281xx/Makefile b/arch/arm/cpu/armv7/bcm281xx/Makefile
index bd867a2..f24aeb3 100644
--- a/arch/arm/cpu/armv7/bcm281xx/Makefile
+++ b/arch/arm/cpu/armv7/bcm281xx/Makefile
@@ -10,3 +10,4 @@
 obj-y	+= clk-sdio.o
 obj-y	+= clk-bsc.o
 obj-$(CONFIG_BCM_SF2_ETH) += clk-eth.o
+obj-y	+= clk-usb-otg.o