stm32mp1: add minimal support for co-processor Cortex-M4

STM32MP1 chip embeds a dual Cortex-A7 and a Cortex-M4.
The support for Cortex-M4 clocks is added when configuring the clock tree.
Some minimal security features to allow communications between A7 and M4
are also added.

Change-Id: I60417e244a476f60a2758f4969700b2684056665
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/plat/st/stm32mp1/bl2_plat_setup.c b/plat/st/stm32mp1/bl2_plat_setup.c
index c7bc39f..2477954 100644
--- a/plat/st/stm32mp1/bl2_plat_setup.c
+++ b/plat/st/stm32mp1/bl2_plat_setup.c
@@ -202,6 +202,9 @@
 		mmio_clrbits_32(rcc_base + RCC_BDCR, RCC_BDCR_VSWRST);
 	}
 
+	/* Disable MCKPROT */
+	mmio_clrbits_32(rcc_base + RCC_TZCR, RCC_TZCR_MCKPROT);
+
 	generic_delay_timer_init();
 
 	if (stm32mp1_clk_probe() < 0) {