eRPC: fix server app build

Change-Id: Iee4bbbe49280e8c4850bab4e00a55a8db2581223
Signed-off-by: David Vincze <david.vincze@arm.com>
diff --git a/erpc/server/app/CMakeLists.txt b/erpc/server/app/CMakeLists.txt
index 68d0cd9..05f4da3 100644
--- a/erpc/server/app/CMakeLists.txt
+++ b/erpc/server/app/CMakeLists.txt
@@ -25,6 +25,8 @@
 include(${CONFIG_SPE_PATH}/platform/cpuarch.cmake)
 # Include common configs exported from TF-M
 include(${CONFIG_SPE_PATH}/cmake/spe_config.cmake)
+# Load platform specific config if exists
+include(${CONFIG_SPE_PATH}/platform/config.cmake OPTIONAL)
 
 include(${TFM_TOOLCHAIN_FILE})