dm: mx6: Adjust mx6sxsabresd to use Kconfig for DM_THERMAL

Use Kconfig instead of board config for DM and DM_THERMAL.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mx6sxsabresd_spl_defconfig b/configs/mx6sxsabresd_spl_defconfig
index 6b36e06..901b01b 100644
--- a/configs/mx6sxsabresd_spl_defconfig
+++ b/configs/mx6sxsabresd_spl_defconfig
@@ -2,3 +2,5 @@
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6SX"
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_MX6SXSABRESD=y
+CONFIG_DM=y
+CONFIG_DM_THERMAL=y