[Liftoff][arm64] Skip unneeded register move

An i64 to i32 conversion within the same register is a noop on arm64,
since i32 operations just use the "W" part of the register anyway.

R=ahaas@chromium.org
CC=rodolph.perfetta@arm.com

Bug: v8:6600
Change-Id: Ia7cb49673c4997dc095736a054d052ffd91bb957
Reviewed-on: https://chromium-review.googlesource.com/1124449Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54175}

src/wasm/baseline/arm64/liftoff-assembler-arm64.h

@@ -628,7 +628,7 @@ bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
                                             LiftoffRegister src, Label* trap) {
   switch (opcode) {
     case kExprI32ConvertI64:
-      Mov(dst.gp().W(), src.gp().W());
+      if (src != dst) Mov(dst.gp().W(), src.gp().W());
       return true;
     case kExprI32SConvertF32:
       Fcvtzs(dst.gp().W(), src.fp().S());  // f32 -> i32 round to zero.