Apply constexpr on global constant varaibles

When HIP_ENABLE_DEFERRED_LOADING=0, many global variables will be
referenced but they are not initialized in that early time. The patch
will use constexpr to initialze global constant varables in compile
time.

Change-Id: I9d538b7abc6a0ce700ec3332b97fc144db5fc1ef

rocclr/device/pal/palprogram.cpp

@@ -170,7 +170,7 @@ bool Segment::freeze(bool destroySysmem) {
   return result;
 }
 
-const static char* Carrizo = "Carrizo";
+static constexpr const char* Carrizo = "Carrizo";
 HSAILProgram::HSAILProgram(Device& device, amd::Program& owner)
     : Program(device, owner),
       rawBinary_(nullptr),