[IntrinsicEmitter] Add overloaded types for SVE intrinsics (Subdivide2 & Subdivide4)

Summary:
Both match the type of another intrinsic parameter of a vector type, but where each element is subdivided to form a vector with more elements of a smaller type.

Subdivide2Argument allows intrinsics such as the following to be defined:
 - declare <vscale x 4 x i32> @llvm.something.nxv4i32(<vscale x 8 x i16>)

Subdivide4Argument allows intrinsics such as:
 - declare <vscale x 4 x i32> @llvm.something.nxv4i32(<vscale x 16 x i8>)

Tests are included in follow up patches which add intrinsics using these types.

Reviewers: sdesmalen, SjoerdMeijer, greened, rovka

Reviewed By: sdesmalen

Subscribers: rovka, tschuett, jdoerfert, cfe-commits, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67549

llvm-svn: 372380