drivers: watchdog: add mcf watchdog support

This watchdog driver applies to the following
mcf families:

- mcf52x2 (5271 5275 5282)
- mcf532x (5329 5373)
- mcf523x (5235)

Cpu's not listed for each family does not have WDT module.

Note, after some attempts testing by qemu on 5208 i
finally abandoned, watchdog seems not implemented properly.

The driver has been tested in a real M5282EVM.

Signed-off-by: Angelo Dureghello <angelo@kernel-space.org>
---
Changes for v2:
- remove unnecessary hardcoded timeouts
- remove unnecessary hw_watchdog_xxx stuff
- rewrite wdog module reg calculation
- using IS_ENABLED() where possible
Changes for v3:
- remove hardcoded 4s test
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 6466635..07fc494 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -178,6 +178,13 @@
 	help
 	  Select this to enable max6370 watchdog timer.
 
+config WDT_MCF
+	bool "ColdFire family watchdog timer support"
+	depends on WDT
+	help
+	  Select this to enable ColdFire watchdog timer,
+	  which supports mcf52x2 mcf532x mcf523x families.
+
 config WDT_MESON_GXBB
 	bool "Amlogic watchdog timer support"
 	depends on WDT