[X86][MC] Reject `call`/`jmp [offset fn_ref]` in Intel syntax

This syntax is confusing and likely invalid. In addition, MASM rejects
it and GAS seems to behave oddly with it. Therefore we shall reject this
syntax for both unconditional `call` and `jmp` instructions, as
discussed in D149579.

Depends on D150047

Differential Revision: https://reviews.llvm.org/D150048