clk: stm32mp1: update the security based on new compatible

From the new binding, the RCC become secured based on the new
compatible. This must be done only from the secure OS initialisation.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I7f0a62f22bfcca638ddaefc9563df00f89f01653
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/188398


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Gabriel FERNANDEZ <gabriel.fernandez@st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>
Reviewed-by: Etienne CARRIERE <etienne.carriere@st.com>