soc: loongson2_pm: add power management support

soc: loongson2_pm: add power management support

The Loongson-2's power management controller was ACPI, supports ACPI
S2Idle (Suspend To Idle), ACPI S3 (Suspend To RAM), ACPI S4 (Suspend To
Disk), ACPI S5 (Soft Shutdown) and supports multiple wake-up methods
(USB, GMAC, PWRBTN, etc.). This driver was to add power management
controller support that base on dts for Loongson-2 series SoCs.

Co-developed-by: Liu Yun <liuyun@loongson.cn>
Signed-off-by: Liu Yun <liuyun@loongson.cn>
Co-developed-by: Liu Peibao <liupeibao@loongson.cn>
Signed-off-by: Liu Peibao <liupeibao@loongson.cn>
Cc: soc@kernel.org
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Link: https://lore.kernel.org/r/20230803063703.5659-3-zhuyinbo@loongson.cn
Signed-off-by: Arnd Bergmann <arnd@arndb.de>