dm: cache: Create a uclass for cache

The cache UCLASS will be used for configure settings that can be found
in a CPU's L2 cache controller.

Add a uclass and a test for cache.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
diff --git a/drivers/Makefile b/drivers/Makefile
index a7bba3e..0a00096 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -77,6 +77,7 @@
 obj-y += block/
 obj-y += board/
 obj-$(CONFIG_BOOTCOUNT_LIMIT) += bootcount/
+obj-y += cache/
 obj-$(CONFIG_CPU) += cpu/
 obj-y += crypto/
 obj-$(CONFIG_FASTBOOT) += fastboot/