shields: x_nucleo_idb05a1: boards: add stm32mp157c_dk2 configuration

Add configuration file for the stm32mp157c_dk2.
Beacon, Central are working.
Peripheral is not compiling because of .elf exceeding FLASH region,
else should be working.

Signed-off-by: Yaël Boutreux <yael.boutreux@st.com>
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>