[arm] Add big-endian version of pcrel fixups for adr instructions

Summary:
In 2e24219d, a number of ARM pcrel fixups were resolved at assembly
time, to solve PR44929. This only covered little-endian ARM however, so
add similar fixups for big-endian ARM. Also extend the test case to
cover big-endian ARM.

Reviewers: hans, psmith, MaskRay

Reviewed By: psmith, MaskRay

Subscribers: kristof.beyls, hiraditya, danielkiss, emaste, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79774