dm: Expand and complete Kconfig in drivers/

Expand the help messages for each driver. Add missing Kconfig for I2C,
SPI flash and thermal.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index e69de29..813d1c2 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -0,0 +1,9 @@
+config DM_CROS_EC
+	bool "Enable Driver Model for Chrome OS EC"
+	depends on DM
+	help
+	  Enable driver model for the Chrome OS EC interface. This
+	  allows the cros_ec SPI driver to operate with CONFIG_DM_SPI
+	  but otherwise makes few changes. Since cros_ec also supports
+	  I2C and LPC (which don't support driver model yet), a full
+	  conversion is not yet possible.