elf: Add elf headers helpers support

ELF header format is been used in multiple places,
add helper functions to get section, program headers, and
string table section details of the elf header.

Change-Id: Ib67b6f25a3a9c32305710eae4ad66bea511d6799
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>