x86-64, NUMA: simplify nodedata allocation

With top-down memblock allocation, the allocation range limits in
ealry_node_mem() can be simplified - try node-local first, then any
node but in any case don't allocate below DMA limit.

Remove early_node_mem() and implement simplified allocation directly
in setup_node_bootmem().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>