hw/loongarch: Add acpi SPCR table support

hw/loongarch: Add acpi SPCR table support

Serial port console redirection table can be used for default serial
port selection, like chosen stdout-path selection with FDT method.

With acpi SPCR table added, early debug console can be parsed from
SPCR table with simple kernel parameter earlycon rather than
earlycon=uart,mmio,0x1fe001e0

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20240907073037.243353-1-maobibo@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>