[lld][ARM][2/3]Big Endian support - Word invariant support

Changes:
 - Adding BE32 big endian Support for Arm.
 - Replace the writele and readle with their endian-aware versions.
 - Adding test cases for the big-endian be32 arm configuration.

     Patch by: Milosz Plichta. This patch merges all the changes from
     this patch https://reviews.llvm.org/D140203 as well.

Reviewed By: peter.smith, MaskRay

Differential Revision: https://reviews.llvm.org/D140202