build_package.sh: keep stm32 files when collecting build artefacts

For STM32MP1 platforms, BL2 is packaged with its DT in an *.stm32 file.
This file is the copied in the first stage boot loader partition of the
boot device.
To ease tests and debug it can be handy to keep this stm32 file in the
build artefacts.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I5888ace39beb42d2a16c7381d26f6b7fc8292438
1 file changed