x86, memblock: Add memblock_x86_memory_in_range()

It will return memory size in specified range according to memblock.memory.region

Try to share some code with memblock_x86_free_memory_in_range() by passing get_free to
__memblock_x86_memory_in_range().

-v2: Ben want _in_range in the name instead of size

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>