eal/ppc: fix mmap for memory initialization

eal/ppc: fix mmap for memory initialization

On IBM POWER platform, when mapping /dev/zero file to hugepage memory
space, mmap will not respect the requested address hint. This will cause
the memory initialization for the second process fails. This patch adds
the required mmap flags to make it work. Beside this, users need to set
the nr_overcommit_hugepages to expand the VA range. When
doing the initialization, users need to set both nr_hugepages and
nr_overcommit_hugepages to the same value, like 64, 128, etc.

Signed-off-by: Chao Zhu <chaozhu@linux.vnet.ibm.com>
Acked-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>