arm64: defconfig: Enable ARM SBSA watchdog driver

Enables ARM generic SBSA compatible watchdog driver for NXP LX2160a SoC.
Enabled as built-in for it is a core feature.

Signed-off-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>