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.cc

@@ -30,11 +30,6 @@ DEFINE_bool(trace_function_references, false,
 DEFINE_bool(trace_function_data, false,
             "Generate tracing for function result data.", "CPU");
 
-DEFINE_bool(
-    disable_global_lock, false,
-    "Disables global lock usage in guest code. Does not affect host code.",
-    "CPU");
-
 DEFINE_bool(validate_hir, false,
             "Perform validation checks on the HIR during compilation.", "CPU");