[M68k][test] Initial migration of MC tests

As the context depicted by bug 49865[1], we are migrating tests under
`test/CodeGen/M68k/Encoding`, which was originally used to test
instruction encoding using MIR file as input, into `test/MC/M68k`. We
are also adding test directives for AsmParser using the same set of
inputs.

Currently we are converting the original MIR test files into assembly
code as well as translating the original LIT "RUN" statement into one
that only uses built-in LLVM tools (i.e. Get rid of `extract-section`).

However, since AsmParser has not completely finished, many of these
original test cases fail. Thus, this patch only migrate test files
that are passed by the current implementation of AsmParser (and
MCCodeEmitter). The remaining tests (under test/CodeGen/M68k/Encoding)
will be ported alone with the patch that fixes the related issues.

[1]: https://bugs.llvm.org/show_bug.cgi?id=49865

Differential Revision: https://reviews.llvm.org/D101410

Author: mshockwave