dm: omap3: Move driver model CONFIGs to Kconfig

Remove driver model CONFIGs from the board config headers and use Kconfig
instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/cpu/armv7/omap3/Kconfig b/arch/arm/cpu/armv7/omap3/Kconfig
index a029379..2fe3232 100644
--- a/arch/arm/cpu/armv7/omap3/Kconfig
+++ b/arch/arm/cpu/armv7/omap3/Kconfig
@@ -93,6 +93,15 @@
 
 endchoice
 
+config DM
+	default y if !SPL_BUILD
+
+config DM_GPIO
+	default y if DM && !SPL_BUILD
+
+config DM_SERIAL
+	default y if DM && !SPL_BUILD
+
 config SYS_SOC
 	default "omap3"