[AArch64] Split fuse-literals feature

This diff splits fuse-literals feature and enables fuse-adrp-add by default,
in particular, it adjusts instruction scheduling to place ADRP+ADD pairs together.
This also enables the linker to apply the relaxations described in
https://github.com/ARM-software/abi-aa/commit/d2ca58c54b8e955cfef25c71822f837ae0439d73.

Differential revision: https://reviews.llvm.org/D120104

Test plan: make check-all