Add new vector types for 512-, 1024- and 2048-bit vectors

Those types are needed to implement instructions for Hexagon Vector
Extensions (HVX): 16x32, 16x64, 32x16, 32x32, 32x64, 64x8, 64x16,
64x32, 128x8, 128x16, 256x8, 512x1, and 1024x1.

llvm-svn: 253923