intel-oneapi-dnn: fix header/lib paths (#23326)

Help dependents find libraries/headers. Like intel-oneapi-mkl, this
package offers several different versions of libraries that conflict.
This PR chooses one of those versions. When
https://github.com/spack/spack/discussions/22749 is resolved, this
package should be updated to choose which libraries to use.

var/spack/repos/builtin/packages/intel-oneapi-dnn/package.py

@@ -31,3 +31,13 @@ class IntelOneapiDnn(IntelOneApiLibraryPackage):
     @property
     def component_dir(self):
         return 'dnnl'
+
+    @property
+    def headers(self):
+        include_path = join_path(self.component_path, 'cpu_dpcpp_gpu_dpcpp', 'include')
+        return find_headers('dnnl', include_path)
+
+    @property
+    def libs(self):
+        lib_path = join_path(self.component_path, 'cpu_dpcpp_gpu_dpcpp', 'lib')
+        return find_libraries(['libdnnl', 'libmkldnn'], root=lib_path, shared=True)