sw64: add support for S3 sleep option

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5XTK7



--------------------------------

The S3 sleeping state is a low wake latency sleeping state where all
system context is lost except system memory. This state will put memory
device controller into self-refresh mode in which the memory device
maintains its stored data without any active command from the memory
controller.

At present, only SW831 supports S3 sleep option and has been tested
successfully on SW831 CRB. BTW, one should upgrade SROM, HMCode and
BIOS firmwares to enable this function.

Signed-off-by: Xu Chenjiao <xuchenjiao@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>