watchdog: qcom: update device tree bindings

Update the compatible string to align with driver and also
add SoC specific string to DTS.

CC: linux-watchdog@vger.kernel.org
Signed-off-by: Matthew McClintock <mmcclint@codeaurora.org>
Signed-off-by: Thomas Pedersen <twp@codeaurora.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>