am335x: add support for cape detect functionality

Update the Kconfig and the board file to make the am335x board compatible
with cape detection.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
diff --git a/arch/arm/mach-omap2/am33xx/Kconfig b/arch/arm/mach-omap2/am33xx/Kconfig
index 9a98e8a..11e54cd 100644
--- a/arch/arm/mach-omap2/am33xx/Kconfig
+++ b/arch/arm/mach-omap2/am33xx/Kconfig
@@ -34,6 +34,7 @@
 	select DM_GPIO
 	select DM_SERIAL
 	select TI_I2C_BOARD_DETECT
+	select SUPPORT_EXTENSION_SCAN
 	imply CMD_DM
 	imply SPL_DM
 	imply SPL_DM_SEQ_ALIAS