[nfc][libomptarget] Inline option into target_impl

Summary:
[nfc][libomptarget] Inline option into target_impl

Subset of D69423. The macros that were in option.h are all target dependent.
Inlining the header simplifies the dependency graph when looking to move code
into a common subdir.

Reviewers: ABataev, jdoerfert, grokos

Subscribers: openmp-commits

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D69472