rdc_field_t replaces uint32_t; centralize field data

Make the RDC use the new rdc_field_t enum instead of uint32_t.
This will help prevent invalid field types from being passed in.

Also, centralize where data related to fields is kept. This will
reduce the number of places where changes are required each
time a new field is added.

Finally, cleaned up several cpplint issues.

Change-Id: I48e4512e18c164411d8b09ae3d4bed99fba359ec

example/field_value_example.cc

@@ -129,7 +129,7 @@ int main(int, char **) {
 
     // Create the field groups to monitor POWER and TEMP
     rdc_field_grp_t field_group_id;
-    uint32_t field_ids[2];
+    rdc_field_t field_ids[2];
     field_ids[0] = RDC_FI_GPU_MEMORY_USAGE;
     field_ids[1] = RDC_FI_POWER_USAGE;
     result = rdc_group_field_create(rdc_handle, 2,