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/cache/Makefile b/drivers/cache/Makefile
new file mode 100644
index 0000000..2ba6806
--- /dev/null
+++ b/drivers/cache/Makefile
@@ -0,0 +1,3 @@
+
+obj-$(CONFIG_CACHE) += cache-uclass.o
+obj-$(CONFIG_SANDBOX) += sandbox_cache.o