memory hotadd 1/7: Setup m2p table for hot-added memory

memory hotadd 1/7: Setup m2p table for hot-added memory

When new memory added to the system, we need to update the m2p table
to cover the new memory range.

When memory add, it is difficult to allocate continous pages, so we
allocate the memory from the new added memory range. This also improve
the locality in numa situation.

We don't support 1G mapping for hot memory, because AFAIK currently
hot-plug memory will not be that large.

Signed-off-by: Jiang, Yunhong <yunhong.jiang@intel.com>