hw/loongarch/virt: Add FDT table support with acpi ged pm register

hw/loongarch/virt: Add FDT table support with acpi ged pm register

ACPI ged is used for power management on LoongArch virt platform, in
general it is parsed from acpi table. However if system boot directly from
elf kernel, no UEFI bios is provided and acpi table cannot be used also.

Here acpi ged pm register is exposed with FDT table, it is compatbile
with syscon method in FDT table, only that acpi ged pm register is accessed
with 8-bit mode, rather with 32-bit mode.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Tested-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20240918014206.2165821-3-maobibo@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>