dm: cros_ec: Convert cros_ec keyboard driver to driver model

Adjust the cros_ec keyboard driver to support driver model. Make this the
default for all Exynos boards so that those that use a keyboard will build
correctly with this driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/Kconfig b/arch/sandbox/Kconfig
index f078c9e..25e316c 100644
--- a/arch/sandbox/Kconfig
+++ b/arch/sandbox/Kconfig
@@ -17,4 +17,7 @@
 	  used on some devices to allow the CPU to communicate with its
 	  peripherals.
 
+config DM_KEYBOARD
+	default y
+
 endmenu