tegra: clock: Support enabling external clocks

Add a simple function to enable external clocks.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/arch/arm/include/asm/arch-tegra/clock.h b/arch/arm/include/asm/arch-tegra/clock.h
index 04011ae..f9dd3c8 100644
--- a/arch/arm/include/asm/arch-tegra/clock.h
+++ b/arch/arm/include/asm/arch-tegra/clock.h
@@ -336,4 +336,12 @@
 
 void tegra30_set_up_pllp(void);
 
+/**
+ * Enable output clock for external peripherals
+ *
+ * @param clk_id	Clock ID to output (1, 2 or 3)
+ * @return 0 if OK. -ve on error
+ */
+int clock_external_output(int clk_id);
+
 #endif  /* _TEGRA_CLOCK_H_ */