eal: add option to delete hugepage backing files

eal: add option to delete hugepage backing files

When an application using huge-pages crash or exists, the hugetlbfs
backing files are not cleaned up. This is a patch to clean those files.
There are multi-process DPDK applications that may be benefited by those
backing files. Therefore, I have made that configurable so that the
application that does not need those backing files can remove them, thus
not changing the current default behavior. The application itself can
clean it up, however the rationale behind DPDK cleaning it up is, DPDK
created it and therefore, it is better it unlinks it.

Signed-off-by: Shesha Sreenivasamurthy <shesha@cisco.com>
Acked-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>