IR: Sort generic intrinsics before target specific ones

This splits out the intrinsic table such that generic intrinsics come
first and target specific intrinsics are grouped by target. From here
we can find out which target an intrinsic is for or differentiate
between generic and target intrinsics.

The motivation here is to make it easier to move target specific
intrinsic handling out of generic code.

llvm-svn: 275575