watchdog: Migrate OMAP_WATCHDOG to Kconfig

Move this entry to Kconfig.  As it is a hardware watchdog, select
HW_WATCHDOG.  While we could default to enabling this for all platforms,
it is currently only enabled by default on AM33XX, so keep that logic
today.

Cc: Roger Meier <r.meier@siemens.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/draco_defconfig b/configs/draco_defconfig
index 2ecdd3c..0e50b31 100644
--- a/configs/draco_defconfig
+++ b/configs/draco_defconfig
@@ -65,3 +65,4 @@
 CONFIG_G_DNL_MANUFACTURER="Siemens AG"
 CONFIG_G_DNL_VENDOR_NUM=0x0908
 CONFIG_G_DNL_PRODUCT_NUM=0x02d2
+CONFIG_OMAP_WATCHDOG=y