enable CMake unity build in build.sh

docker/build.sh

@@ -65,6 +65,7 @@ CmakeGenerate() {
     -S "$SOURCES_DIR" \
     -B "$BUILD_DIR" \
     -DCMAKE_BUILD_TYPE=$BUILD_TYPE \
+    -DCMAKE_UNITY_BUILD="ON" \
     -DARM_NONE_EABI_TOOLCHAIN_PATH="$TOOLS_DIR/$GCC_ARM_PATH" \
     -DNRF5_SDK_PATH="$TOOLS_DIR/$NRF_SDK_VER" \
     -DBUILD_DFU=1 \