[ARM] Enable ARMCodeGenPrepare by default

We've had the pass enabled downstream for a couple of weeks and it
seems to be okay, so enable it by default.

Differential Revision: https://reviews.llvm.org/D51920

llvm-svn: 341932

llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp

@@ -42,7 +42,7 @@
 using namespace llvm;
 
 static cl::opt<bool>
-DisableCGP("arm-disable-cgp", cl::Hidden, cl::init(true),
+DisableCGP("arm-disable-cgp", cl::Hidden, cl::init(false),
            cl::desc("Disable ARM specific CodeGenPrepare pass"));
 
 static cl::opt<bool>