[clang][driver][ARM] Clean up ARM target & feature checking in clang driver.

Summary:
- Similar to other targets, instead of passing a toolchain, a driver
  argument should be passed into `arm::getARMTargetFeatures`. Aslo, that
  routine should honor the specified triple. Refactor
  `arm::getARMFloatABI` with 2 separate interfaces. One has the original
  parameters and the other uses the driver and the specified triple.
- That fixes an issue when target & features are queried during the
  offload compilation, where the specified triple should be checked
  instead of a effective triple. A previously failed test is re-enabled.

Subscribers: kristof.beyls, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D74020