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/include/asm/kona-common/clk.h b/arch/arm/include/asm/kona-common/clk.h
index 2c7e829..a5e2fd9 100644
--- a/arch/arm/include/asm/kona-common/clk.h
+++ b/arch/arm/include/asm/kona-common/clk.h
@@ -25,5 +25,6 @@
 struct clk *clk_get_parent(struct clk *clk);
 int clk_sdio_enable(void *base, u32 rate, u32 *actual_ratep);
 int clk_bsc_enable(void *base);
+int clk_usb_otg_enable(void *base);
 
 #endif