arm64/numa: remove the limitation that cpu0 must bind to node0

1. Remove the old binding code.
2. Read the nid of cpu0 from dts.
3. Fallback the nid of cpu0 to 0 when numa=off is set in bootargs.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>