xgl: update xglDbg.h for XGL_INSTANCE

Add XGL_INSTANCE as the first parameter of xglDbgRegisterMsgCallback(),
xglDbgUnregisterMsgCallback(), and xglDbgSetGlobalOption().

The loader is simplified.  loader_log() is modified to always output to
stderr.

glave is modified to register its message callback after xglEnumerateGpus(),
and xglDbgUnregisterMsgCallback() is called only before xglDestroyInstance().

XGL_INSTANCE is ignored by the layers and the driver for now.

Bump up API version to XGL_MAKE_VERSION(0, 56, 1).
diff --git a/icd/intel/instance.c b/icd/intel/instance.c
index 7b7c50b..294bd9a 100644
--- a/icd/intel/instance.c
+++ b/icd/intel/instance.c
@@ -216,6 +216,7 @@
 }
 
 ICD_EXPORT XGL_RESULT XGLAPI xglDbgRegisterMsgCallback(
+    XGL_INSTANCE                                instance,
     XGL_DBG_MSG_CALLBACK_FUNCTION               pfnMsgCallback,
     void*                                       pUserData)
 {
@@ -223,12 +224,14 @@
 }
 
 ICD_EXPORT XGL_RESULT XGLAPI xglDbgUnregisterMsgCallback(
+    XGL_INSTANCE                                instance,
     XGL_DBG_MSG_CALLBACK_FUNCTION               pfnMsgCallback)
 {
     return icd_logger_remove_callback(pfnMsgCallback);
 }
 
 ICD_EXPORT XGL_RESULT XGLAPI xglDbgSetGlobalOption(
+    XGL_INSTANCE                                instance,
     XGL_DBG_GLOBAL_OPTION                       dbgOption,
     size_t                                      dataSize,
     const void*                                 pData)