TableGen: Type-check BinOps

Additionally, allow more than two operands to !con, !add, !and, !or
in the same way as is already allowed for !listconcat and !strconcat.

Change-Id: I9659411f554201b90cd8ed7c7e004d381a66fa93

Differential revision: https://reviews.llvm.org/D44112

llvm-svn: 327494