CodeGen: Use MachineInstr& in TargetInstrInfo, NFC

This is mostly a mechanical change to make TargetInstrInfo API take
MachineInstr& (instead of MachineInstr* or MachineBasicBlock::iterator)
when the argument is expected to be a valid MachineInstr.  This is a
general API improvement.

Although it would be possible to do this one function at a time, that
would demand a quadratic amount of churn since many of these functions
call each other.  Instead I've done everything as a block and just
updated what was necessary.

This is mostly mechanical fixes: adding and removing `*` and `&`
operators.  The only non-mechanical change is to split
ARMBaseInstrInfo::getOperandLatencyImpl out from
ARMBaseInstrInfo::getOperandLatency.  Previously, the latter took a
`MachineInstr*` which it updated to the instruction bundle leader; now,
the latter calls the former either with the same `MachineInstr&` or the
bundle leader.

As a side effect, this removes a bunch of MachineInstr* to
MachineBasicBlock::iterator implicit conversions, a necessary step
toward fixing PR26753.

Note: I updated WebAssembly, Lanai, and AVR (despite being
off-by-default) since it turned out to be easy.  I couldn't run tests
for AVR since llc doesn't link with it turned on.

llvm-svn: 274189
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.h b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.h
index 98be695..70810f1 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.h
@@ -34,13 +34,13 @@
 
   const WebAssemblyRegisterInfo &getRegisterInfo() const { return RI; }
 
-  bool isReallyTriviallyReMaterializable(const MachineInstr *MI,
+  bool isReallyTriviallyReMaterializable(const MachineInstr &MI,
                                          AliasAnalysis *AA) const override;
 
   void copyPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
                    const DebugLoc &DL, unsigned DestReg, unsigned SrcReg,
                    bool KillSrc) const override;
-  MachineInstr *commuteInstructionImpl(MachineInstr *MI, bool NewMI,
+  MachineInstr *commuteInstructionImpl(MachineInstr &MI, bool NewMI,
                                        unsigned OpIdx1,
                                        unsigned OpIdx2) const override;