Add files and directories regex "stm32" and "stm" in "ARM STM STM32MP"
platform to avoid missing files or drivers supported by the
STMicroelectronics series STM32MP15x.

This patch adds the rules already used in Linux kernel for
ARM/STM32 ARCHITECTURE.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>