sandbox: pch: Add a test for the PCH uclass

This uclass currently has no tests. Add a sandbox driver and some simple
tests to provide basic coverage.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: Use "sandbox,pch" for the compatible string, for consistency]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/pch/Makefile b/drivers/pch/Makefile
index 696cdff..8ea6b78 100644
--- a/drivers/pch/Makefile
+++ b/drivers/pch/Makefile
@@ -3,3 +3,4 @@
 obj-y += pch-uclass.o
 obj-y += pch7.o
 obj-y += pch9.o
+obj-$(CONFIG_SANDBOX) += sandbox_pch.o