[M68k] Add codegen support for basic floating point instructions

[mshockwave]

Add codegen supports for instructions created in #61802 #61803 and #61804

[llvmbot]

@llvm/issue-subscribers-backend-m68k

[glaubitz]

Any plans for getting this implemented? Floating point support seems to be the next big blocker for building the Rust compiler for m68k.