[M68k] Do not pass llvm::Function& to M68kCCState

Previously we're passing `llvm::Function&` into `M68kCCState` to lower
arguments in fastcc. However, that reference might not be available if
it's a library call and we only need its argument types. Therefore,
now we're simply passing a list of argument llvm::Type-s.

This fixes PR-50752.

Differential Revision: https://reviews.llvm.org/D108101