rtc: m41t93: Add watchdog support

rtc: m41t93: Add watchdog support

Implement watchdog feature for m41t93 rtc with 1s resolution.
Implement alarm only support (WDIOF_ALARMONLY) in this commit.
Define start, stop, ping, and set_timeout callbacks as needed
by the watchdog framework.

Use selftests/watchdog/watchdog-test kselftest for testing.
Observed IRQ pin(12) of rtc chip going low after late pinging
the watchdog.

Signed-off-by: Akhilesh Patil <akhilesh@ee.iitb.ac.in>
Link: https://patch.msgid.link/77c2e9f4ab0811a919595d7a5476b00abd1c2803.1758379856.git.akhilesh@ee.iitb.ac.in
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>