icd: clean up alloc functions

Clean up and move alloc functions to icd-alloc.[ch].
diff --git a/icd/intel/intel.c b/icd/intel/intel.c
index 538a482..15d126d 100644
--- a/icd/intel/intel.c
+++ b/icd/intel/intel.c
@@ -92,7 +92,7 @@
 
     intel_debug_init();
 
-    ret = icd_set_allocator(pAllocCb);
+    ret = icd_allocator_init(pAllocCb);
     if (ret != XGL_SUCCESS)
         return ret;