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 <[email protected]>
Signed-off-by: Liu Yun <[email protected]>
Co-developed-by: Liu Peibao <[email protected]>
Signed-off-by: Liu Peibao <[email protected]>
Cc: [email protected]
Cc: Ulf Hansson <[email protected]>
Signed-off-by: Yinbo Zhu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnd Bergmann <[email protected]>