[mips] Make unalignedload.ll test stricter and easier to modify for MIPS32r6/MIPS64r6

Summary:
* Split into two functions, one to test each struct.
* R0 and R2 must be defined by an lw with a %got reference to the correct
  symbol.
* Test for $4 (first argument) where appropriate instead of accepting any
  register.
* Test that the two lbu's are correctly combined into $4

Depends on D3844

Reviewers: jkolek, zoran.jovanovic, vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3845

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209424 91177308-0d34-0410-b5e6-96231b3b80d8
ARM64: separate load/store operands to simplify assembler

This changes ARM64 to use separate operands for each component of an
address, and look for separate '[', '$Rn, ..., ']' tokens when
parsing.

This allows us to do away with quite a bit of special C++ code to
handle monolithic "addressing modes" in the MC components. The more
incremental matching of the assembler operands also allows for better
diagnostics when LLVM is presented with invalid input.

Most of the complexity here is with the register-offset instructions,
which were extremely dodgy beforehand: even when the instruction used
wM, LLVM's model had xM as an operand. We papered over this
discrepancy before, but that approach doesn't work now so I split them
into separate X and W variants.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209425 91177308-0d34-0410-b5e6-96231b3b80d8
ARM64: model pre/post-indexed operations properly.

We should be keeping track of the writeback on these instructions,
otherwise we're relying on LLVM's stupidity for correct code.

Fortunately, the MC layer can now handle all required constraints,
which means we can get rid of the CodeGen only PseudoInsts too.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209426 91177308-0d34-0410-b5e6-96231b3b80d8
Yes they do

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209429 91177308-0d34-0410-b5e6-96231b3b80d8
ARM64: these work too

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209430 91177308-0d34-0410-b5e6-96231b3b80d8