LoongArch: Add suspend (ACPI S3) support

Add suspend (Suspend To RAM, aka ACPI S3) support for LoongArch.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Clean up loongson3_smp_ops declaration

Since loongson3_smp_ops is not used in LoongArch anymore, let's remove
it for cleanup.

Fixes: f2ac457a6138 ("LoongArch: Add CPU definition headers")
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Remove unused variables

There are some variables never used or referenced, this patch
removes these varaibles and make the code cleaner.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Use ABI names of registers where appropriate

Some of the assembly in the LoongArch port seem to come from a
prehistoric time, when the assembler didn't even have support for the
ABI names we all come to know and love, thus used raw register numbers
which hampered readability.

The usages are found with a regex match inside arch/loongarch, then
manually adjusted for those non-definitions.

Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Add CPU definition headers

Add common headers (CPU definition and address space layout) for basic
LoongArch support.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>