[WebAssembly] Made assembler only use stack instruction tablegen defs

Summary:
This ensures we have the non-register version of the instruction.

The stack version of call_indirect now wants a type index argument,
so that has been added in the existing tests.

Tested:
llvm-lit -v `find test -name WebAssembly`

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, aheejin, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D51662

llvm-svn: 342753