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/configs/sandbox_vpl_defconfig b/configs/sandbox_vpl_defconfig
index be8186e..c31adbb 100644
--- a/configs/sandbox_vpl_defconfig
+++ b/configs/sandbox_vpl_defconfig
@@ -74,6 +74,7 @@
 CONFIG_CMD_PCI=y
 CONFIG_CMD_REMOTEPROC=y
 CONFIG_CMD_SPI=y
+CONFIG_CMD_TEMPERATURE=y
 CONFIG_CMD_USB=y
 CONFIG_BOOTP_DNS2=y
 CONFIG_CMD_TFTPPUT=y
@@ -223,6 +224,7 @@
 CONFIG_SYSRESET=y
 CONFIG_SPL_SYSRESET=y
 CONFIG_TPL_SYSRESET=y
+CONFIG_DM_THERMAL=y
 CONFIG_TIMER=y
 CONFIG_TIMER_EARLY=y
 CONFIG_SANDBOX_TIMER=y