arm64: dts: renesas: falcon: Move watchdog config to CPU board DTS

The 32 kHz oscillator driving the R-Car V3U watchdog is located on the
Falcon CPU board.  Hence move the watchdog configuration from the main
Falcon DTS file to the DTS file that describes the CPU board.

Fixes: d207dc50 ("arm64: dts: renesas: falcon: Enable watchdog timer")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20210316154705.2433528-3-geert+renesas@glider.be