clk: tegra: Implement memory-controller clock

The memory controller clock runs either at half or the same frequency as
the EMC clock.

Reviewed-By: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

include/dt-bindings/clock/tegra20-car.h

@@ -49,7 +49,7 @@
 /* 30 */
 #define TEGRA20_CLK_CACHE2 31
 
-#define TEGRA20_CLK_MEM 32
+#define TEGRA20_CLK_MC 32
 #define TEGRA20_CLK_AHBDMA 33
 #define TEGRA20_CLK_APBDMA 34
 /* 35 */