drivers: watchdog: add system calls

wdt_install_timeout() was skipped as it installs an ISR-context
callback handler function. The rest are simple wrappers.

Added myself as the maintainer of the syscall handlers. WDT
subsystem appears to not currently have an owner.

Fixes: #21432

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
Signed-off-by: Anas Nashif <anas.nashif@intel.com>