boards: renesas: add support for watchdog driver on Renesas RA boards

Enable support of watchdog driver on these boards:
- RA8: ek_ra8m1, ek_ra8d1, mck_ra8t1
- RA6: ek_ra6e2, ek_ra6m1, ek_ra6m2, ek_ra6m3, ek_ra6m4, ek_ra6m5,
  fpb_ra6e1, fpb_ra6e2
- RA4: ek_ra4l1, ek_ra4e2, ek_ra4m1, ek_ra4m2, ek_ra4m3, ek_ra4w1,
  fpb_ra4e1, voice_ra4e1
- RA2: ek_ra2a1, ek_ra2l1

Signed-off-by: The Nguyen <the.nguyen.yf@renesas.com>