DetectorsRaw: place the RDH constants in the constant address space

MSL requires every variable at program scope, class-scope statics included, to
name an address space. GPUglobalconstexpr() expands to constexpr everywhere
except Metal, so this is a no-op for host, CUDA, HIP, OpenCL and cling.

These were missed by the earlier pass: the header they sit in only started
being compiled once the errors ahead of it were gone.

Author: ktf

Detectors/Raw/include/DetectorsRaw/RDHUtils.h

@@ -51,8 +51,8 @@ struct RDHUtils {
   using RDHv6 = o2::header::RAWDataHeaderV6;
   using RDHv7 = o2::header::RAWDataHeaderV7; // update this for every new version
 
-  static constexpr int GBTWord128 = 16; // length of GBT word
-  static constexpr int MAXCRUPage = 512 * GBTWord128;
+  static GPUglobalconstexpr() int GBTWord128 = 16; // length of GBT word
+  static GPUglobalconstexpr() int MAXCRUPage = 512 * GBTWord128;
   /// get numeric version of the RDH
 
   ///_______________________________