Introduce driver for WDG block on ROHM BD96801 scalable PMIC.

This driver only supports watchdog with I2C feeding and delayed
response detection. Whether the watchdog toggles PRSTB pin or
just causes an interrupt can be configured via device-tree.

The BD96801 PMIC HW supports also window watchdog (too early
feeding detection) and Q&A mode. These are not supported by
this driver.
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/bb3a49d606e793a61b0c033170ff2a9f30f3c2a5.1719473802.git.mazziesaccount@gmail.comSigned-off-by: Lee Jones <lee@kernel.org>