[Driver] Add defaults for Android ARM FPUs.

Summary:
Android mandates that devices have at least vfpv3-d16 until
Marshmallow and NEON after that. Still honor the user's decision, but
raise the defaults for Android targets.

Reviewers: srhines, pirama, javed.absar, kristof.beyls, peter.smith

Reviewed By: peter.smith

Subscribers: peter.smith, rengolin, kristof.beyls, chrib, cfe-commits

Differential Revision: https://reviews.llvm.org/D53121

llvm-svn: 344367