Tidy x86 assembler.

Use helper functions to compute when the kind has a SIB, a ModRM and RegReg
form.

Change-Id: I86a5cb944eec62451c63281265e6974cd7a08e07
diff --git a/compiler/dex/quick/arm/assemble_arm.cc b/compiler/dex/quick/arm/assemble_arm.cc
index a895e6e..5083bbc 100644
--- a/compiler/dex/quick/arm/assemble_arm.cc
+++ b/compiler/dex/quick/arm/assemble_arm.cc
@@ -1628,7 +1628,7 @@
   CreateNativeGcMap();
 }
 
-int ArmMir2Lir::GetInsnSize(LIR* lir) {
+size_t ArmMir2Lir::GetInsnSize(LIR* lir) {
   DCHECK(!IsPseudoLirOp(lir->opcode));
   return EncodingMap[lir->opcode].size;
 }