thermal: add sandbox driver

Provide a simple sandbox driver for the thermal uclass.
It simply registers and returns 100 degrees C if requested.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
index 15fe847..8acc7d2 100644
--- a/drivers/thermal/Makefile
+++ b/drivers/thermal/Makefile
@@ -4,6 +4,7 @@
 # Author: Nitin Garg <nitin.garg@freescale.com>
 
 obj-$(CONFIG_DM_THERMAL) += thermal-uclass.o
+obj-$(CONFIG_SANDBOX) += thermal_sandbox.o
 obj-$(CONFIG_IMX_THERMAL) += imx_thermal.o
 obj-$(CONFIG_IMX_SCU_THERMAL) += imx_scu_thermal.o
 obj-$(CONFIG_TI_DRA7_THERMAL) += ti-bandgap.o