fix(build): Allow to regenerate files using zap

For the record, files can be regenerated from developer using:

  rm -rf build ; cmake_options=-DZAP_GENERATE=ON ./helper.mk

For some reasons developer will have to commit also generated files,
which is a bad practice, but I believe it was intentional to avoid
propagation to zap as build dependency, this may be revised to avoid
serialization of development.

Relate-to: https://github.com/project-chip/zap/releases/download/v2025.07.24/zap-linux-x64.deb
Bug-SiliconLabs: UIC-3222
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr

helper.mk

@@ -16,7 +16,7 @@ project?=unifysdk
 BUILD_DEV_GUI?=OFF
 BUILD_IMAGE_PROVIDER?=ON
 
-cmake_options?=-B ${build_dir}
+cmake_options+=-B ${build_dir}
 
 CMAKE_GENERATOR?=Ninja
 export CMAKE_GENERATOR