watchdog: pnx4008: cleanup resource handling using managed devices

The resource handling in this driver was flaky: IO_ADDRESS instead of
ioremap (and no unmapping), an unneeded static resource, no central exit
path for error cases. Fix this by converting the driver to use managed
resources. Also use dev_*-messages instead of pr_* while we are here.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>