refactor(arm): switch to rse_mbx_init

The rse_comms_init() function will be removed. The new function to use
is rse_mbx_init() for the MHU mailbox initialization.

Change-Id: I1932500ef71b6e895f0ee164ee9c2b58becf4409
Signed-off-by: Yann Gautier <yann.gautier@st.com>
2 files changed