MIPS: Loongson64: Distinguish firmware dependencies DTB/LEFI

Add DTB boot support, only support Loongson-2K1000 processor
for now, determine whether to use the built-in DTB or the DTB
from the firmware by checking the range of CKSEG0 and XKPHYS.
loongson_fw_interface will be used in the future.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Tested-by: Ming Wang <wangming01@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>