[SystemZ] Add missing vector instructions for the assembler

Most z13 vector instructions have a base form where the data type of
the operation (whether to consider the vector to be 16 bytes, 8
halfwords, 4 words, or 2 doublewords) is encoded into a mask field,
and then a set of extended mnemonics where the mask field is not
present but the data type is encoded into the mnemonic name.

Currently, LLVM only supports the type-specific forms (since those
are really the ones needed for code generation), but not the base
type-generic forms.

To complete the assembler support and make it fully compatible with
the GNU assembler, this commit adds assembler aliases for all the
base forms of the various vector instructions.

It also adds two more alias forms that are documented in the PoP:
VFPSO/VFPSODB/WFPSODB -- generic form of VFLCDB etc.
VNOT -- special variant of VNO

llvm-svn: 284586