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>
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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