[LLD][ELF][ARM] Add test cases for R_ARM_THM_MOV*-type relocs

Summary: This patch adds missing tests cases for R_ARM_THM_MOVW/MOVT* relocations for the sake of completeness.

Reviewers: peter.smith, MaskRay, espindola, psmith

Reviewed By: MaskRay, psmith

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

Tags: #llvm, #lld

Differential Revision: https://reviews.llvm.org/D74827