malloc: support contiguous allocation

malloc: support contiguous allocation

No major changes, just add some checks in a few key places, and
a new parameter to pass around.

Also, add a function to check malloc element for physical
contiguousness. For now, assume hugepage memory is always
contiguous, while non-hugepage memory will be checked.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Tested-by: Santosh Shukla <santosh.shukla@caviumnetworks.com>
Tested-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Tested-by: Gowrishankar Muthukrishnan <gowrishankar.m@linux.vnet.ibm.com>