x86, memblock: Fix early_node_mem with big reserved region.

Xen can reserve huge amounts of memory for pre-ballooning, but that
still shows as RAM in the e820 memory map.  early_node_mem could not
find range because of start/end adjusting, and will go through the
fallback path.  However, the fallback patch is still using
memblock_x86_find_range_node(), and it is partially top-down because
it go through active_range entries from low to high.

Let's use memblock_find_in_range instead memblock_x86_find_range_node.
So get real top down in fallback path.

We may still need to make memblock_x86_find_range_node to do overall
top_down work.

Reported-by: Jeremy Fitzhardinge <jeremy@goop.org>
Tested-by: Jeremy Fitzhardinge <jeremy@goop.org>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <4CC9A9C9.8020700@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>