Use the IntrinsicKind to look up Metal intrinsic calls.

We no longer need to maintain a separate mapping table of intrinsic
function names in Metal.

Change-Id: Ib14b76d3a47a396c4a09adb11e0fd3c144501032
Bug: skia:11961
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/405236
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
2 files changed