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/test/dm/Makefile b/test/dm/Makefile
index 1b08996..49857c5 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -30,6 +30,7 @@
 obj-$(CONFIG_OSD) += osd.o
 obj-$(CONFIG_DM_VIDEO) += panel.o
 obj-$(CONFIG_DM_PCI) += pci.o
+obj-$(CONFIG_PCH) += pch.o
 obj-$(CONFIG_PHY) += phy.o
 obj-$(CONFIG_POWER_DOMAIN) += power-domain.o
 obj-$(CONFIG_DM_PWM) += pwm.o