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/Makefile b/drivers/watchdog/Makefile
index fd5d9c7..eef786f 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -31,6 +31,7 @@
 obj-$(CONFIG_WDT_FTWDT010) += ftwdt010_wdt.o
 obj-$(CONFIG_WDT_GPIO) += gpio_wdt.o
 obj-$(CONFIG_WDT_MAX6370) += max6370_wdt.o
+obj-$(CONFIG_WDT_MCF) += mcf_wdt.o
 obj-$(CONFIG_WDT_MESON_GXBB) += meson_gxbb_wdt.o
 obj-$(CONFIG_WDT_MPC8xxx) += mpc8xxx_wdt.o
 obj-$(CONFIG_WDT_MT7620) += mt7620_wdt.o