[yaml2obj][obj2yaml] - Add a support for SHT_ARM_EXIDX section.

This adds the support for SHT_ARM_EXIDX sections to obj2yaml/yaml2obj tools.

SHT_ARM_EXIDX is a ARM specific index table filled with entries.
Each entry consists of two 4-bytes values (words).
(https://developer.arm.com/documentation/ihi0038/c/?lang=en#index-table-entries)

Differential revision: https://reviews.llvm.org/D88228