mem: fix anonymous mapping on Power9

mem: fix anonymous mapping on Power9

Removed the use of MAP_HUGETLB for anonymous mapping on ppc64.  The
MAP_HUGETLB had previously been added to workaround issues on IBM Power8
systems when mapping /dev/zero.
In the current code the MAP_HUGETLB flag will cause the anonymous mapping
to fail on Power9.
Note, Power8 is currently failing to correctly mmap Hugepages, with and
without this change.

Fixes: 284ae3e9ff9a ("eal/ppc: fix mmap for memory initialization")

Signed-off-by: David Wilder <dwilder@us.ibm.com>
Reviewed-by: Pradeep Satyanarayana <pradeep@us.ibm.com>