[1/6] ARM Neon Intrinsic Tablegen Test Generator.

Changes necessary to arm_neon.td for the generation of Neon tests.

This is the first of six patches to add to the arm neon tablegen
generator the capability of generating tests to verify that the various
ARM intrinsics are implemented properly.

The changes include such items as:
  1. Adding attributes to the Inst record so that additional metadata that is only
     needed for the tests can be specified in TableGen.
  2. Adding wrapper classes for operator (i.e. ``Op'') intrinsics which before
     were simply notates as Inst. This allows us to classify what sort of test
     to generate for said intrinsic and further since the classes do not effect
     the behavior of the Inst base class, allow for normal functioning.

Reviewed by Bob Wilson.