LoongArch: Preserve firmware configuration when desired

If we must preserve the firmware resource assignments, claim the existing
resources rather than reassigning everything.

According to PCI Firmware Specification: if ACPI DSM#5 function returns
0, the OS must retain the resource allocation for PCI in the firmware; if
ACPI DSM#5 function returns 1, the OS can ignore the resource allocation
for PCI and reallocate it.

Signed-off-by: Qihang Gao <gaoqihang@loongson.cn>
Signed-off-by: Juxin Gao <gaojuxin@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>