[AArch64][SVE] Asm: More concise test format

Change the test format for SVE assembler/disassembler tests to be less verbose and have both tests in the same file.

The tests check the following:

 * All instructions are assembled correctly into the right encoding.
 * All instructions are disassembled correctly (into the preferred assembly format)
 * Without -mattr=+sve the instructions are not assembled.
 * Without -mattr=+sve the instructions are not disassembled.

This patch also adds several negative tests for SVE add/sub.


Patch by Sander De Smalen.

Reviewed by: rengolin, fhahn

Differential Revision: https://reviews.llvm.org/D39792

llvm-svn: 317894