AMDGPU: Move dot intrinsic patterns to instruction def

AMDGPU: Move dot intrinsic patterns to instruction def

I tried to use some of the new tablegen features to avoid creating
different operand list permutations, but I still don't see a way to
programmatically build a source pattern dag.

Also add GlobalISel tests, which now all import successfully.

Some of the fneg fold tests are incorrect, which need to be fixed in a
future commit