Add support for /dev/watchdog ioctls

Add support for /dev/watchdog ioctls

* watchdog_ioctl.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* defs.h (DECL_IOCTL): Add watchdog.
* ioctl.c (ioctl_decode): Add 'W' case.
* xlat/watchdog_ioctl_cmds.in: New file.
* tests/ioctl_watchdog.c: New file.
* tests/.gitignore: Add ioctl_watchdog.
* tests/pure_executables.list: Likewise.
* tests/gen_tests.in (ioctl_watchdog): New entry.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>