drivers: wdt: add watchdog driver support for NPCX7 series.

In npcx7 series, the Timer and Watchdog module (TWD) generates the
clocks and interrupts used for timing periodic functions in the system.
It also provides watchdog reset signal generation in response to a
failure detection.

The CL also includes:
    — Add npcx watchdog device tree declarations.
    — Zephyr watchdog api implementation.
    — Add Watchdog definitions for npcx7 series in
      tests/drivers/watchdog/wdt_basic_api/src/test_wdt.c for
      supporting test suites.

Signed-off-by: Mulin Chao <MLChao@nuvoton.com>