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/mips/assemble_mips.cc b/compiler/dex/quick/mips/assemble_mips.cc
index b26ab57..c7e9190 100644
--- a/compiler/dex/quick/mips/assemble_mips.cc
+++ b/compiler/dex/quick/mips/assemble_mips.cc
@@ -709,7 +709,7 @@
   return res;
 }
 
-int MipsMir2Lir::GetInsnSize(LIR* lir) {
+size_t MipsMir2Lir::GetInsnSize(LIR* lir) {
   DCHECK(!IsPseudoLirOp(lir->opcode));
   return EncodingMap[lir->opcode].size;
 }