acpi/arm64: Add SBSA Generic Watchdog support in GTDT driver

This driver adds support for parsing SBSA Generic Watchdog timer
in GTDT, parse all info in SBSA Generic Watchdog Structure in GTDT,
and creating a platform device with that information.

This allows the operating system to obtain device data from the
resource of platform device. The platform device named "sbsa-gwdt"
can be used by the ARM SBSA Generic Watchdog driver.

Signed-off-by: Fu Wei <fu.wei@linaro.org>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Tested-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>