mailbox: introduce stm32-ipcc driver

On STM32 family, the IPCC peripheral allows the communication
between 2 processors offering doorbells mechanism.

Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Loic Pallardy <loic.pallardy@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
3 files changed