ARM: dts: i.MX6: configure L2 cache data and tag latency

Configure the data and tag latency for the L2 cache. This improves the
system performance.

This configuration is taken from Freescale's kernel patch

"ENGR00153601 [MX6]Adjust L2 cache parameter" [1]

which does

writel(0x132, IO_ADDRESS(L2_BASE_ADDR + L2X0_TAG_LATENCY_CTRL));
writel(0x132, IO_ADDRESS(L2_BASE_ADDR + L2X0_DATA_LATENCY_CTRL));

In this patch we are doing the same via the device tree.
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

[1] http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/commit/arch/arm/mach-mx6/mm.c?h=imx_3.0.35_12.09.01&id=814656410b40c67a10b25300e51b0477b2bb96d1

arch/arm/boot/dts/imx6qdl.dtsi

@@ -106,6 +106,8 @@ L2: l2-cache@00a02000 {
 			interrupts = <0 92 0x04>;
 			cache-unified;
 			cache-level = <2>;
+			arm,tag-latency = <4 2 3>;
+			arm,data-latency = <4 2 3>;
 		};
 
 		pmu {