setup initial value of MSR on ppc context

Fixed PrefetchW feature check
Added prefetchw check to startup AVX check, there should be no CPUs that support AVX but not PrefetchW.
Init VRSAVE to all ones.
Removed unused disable_global_lock flag.

src/xenia/cpu/cpu_flags.h

@@ -22,8 +22,6 @@ DECLARE_bool(trace_function_coverage);
 DECLARE_bool(trace_function_references);
 DECLARE_bool(trace_function_data);
 
-DECLARE_bool(disable_global_lock);
-
 DECLARE_bool(validate_hir);
 
 DECLARE_uint64(pvr);