[GISel] Pass MD_callees metadata down in call lowering.

Summary:
This will make it possible to improve IPRA by taking into account
register usage in indirect calls.

NFC yet; this is just laying the groundwork to start building
up patches to take advantage of the information for improved register
allocation.

Reviewers: aditya_nandakumar, volkan, qcolombet, arsenm, rovka, aemerson, paquette

Subscribers: sdardis, wdng, javed.absar, hiraditya, jrtc27, atanasyan, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65488

llvm-svn: 367476