ARM: dts: fix PCLK name on Gemini and MOXA ART

These platforms provide a clock to their watchdog, in each
case this is the peripheral clock (PCLK), so explicitly
name the clock in the device tree.

Take this opportunity to add the "faraday,ftwdt010"
compatible as fallback to the watchdog IP blocks.

Cc: Jonas Jensen <jonas.jensen@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>