[Hardware][PowerPC] Make oneDNN dependency optional for Power (vllm-project#9039)

Signed-off-by: Varad Ahirwadkar <varad.ahirwadkar1@ibm.com>
Signed-off-by: Sumit Dubey <sumit.dubey2@ibm.com>

Author: varad-ahirwadkar

cmake/cpu_extension.cmake

@@ -84,7 +84,12 @@ endif()
 
 message(STATUS "CPU extension compile flags: ${CXX_COMPILE_FLAGS}")
 
-list(APPEND LIBS dnnl numa)
+list(APPEND LIBS numa)
+
+# Appending the dnnl library for the AVX2 and AVX512, as it is not utilized by Power architecture.
+if (AVX2_FOUND OR AVX512_FOUND)
+    list(APPEND LIBS dnnl)
+endif()
 
 #
 # _C extension