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_spl_defconfig b/configs/sandbox_spl_defconfig
index c33f171..af5092b 100644
--- a/configs/sandbox_spl_defconfig
+++ b/configs/sandbox_spl_defconfig
@@ -62,6 +62,7 @@
 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
@@ -216,6 +217,7 @@
 CONFIG_SYSINFO_GPIO=y
 CONFIG_SYSRESET=y
 CONFIG_SPL_SYSRESET=y
+CONFIG_DM_THERMAL=y
 CONFIG_TIMER=y
 CONFIG_TIMER_EARLY=y
 CONFIG_SANDBOX_TIMER=y