armv7: add PL310 support to u-boot

PL310 is the L2$ controller from ARM used in many SoCs
including the Cortex-A9 based OMAP4430

Add support for some of the key PL310 operations
	- Invalidate all
	- Invalidate range
	- Flush(clean & invalidate) all
	- Flush range

Signed-off-by: Aneesh V <aneesh@ti.com>
diff --git a/README b/README
index 7ee1632..2da0f96 100644
--- a/README
+++ b/README
@@ -465,6 +465,12 @@
 		CONFIG_SYS_DCACHE_OFF - Do not enable data cache in U-Boot
 		CONFIG_SYS_L2CACHE_OFF- Do not enable L2 cache in U-Boot
 
+- Cache Configuration for ARM:
+		CONFIG_SYS_L2_PL310 - Enable support for ARM PL310 L2 cache
+				      controller
+		CONFIG_SYS_PL310_BASE - Physical base address of PL310
+					controller register space
+
 - Serial Ports:
 		CONFIG_PL010_SERIAL