stm32mp1: split clkfunc code

Create a new file stm32mp_clkfunc.c to put functions that could be common
between several platforms.

Change-Id: Ica915c796b162b2345056b33328acc05035a242c
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/drivers/st/gpio/stm32_gpio.c b/drivers/st/gpio/stm32_gpio.c
index 5733046..343ad6c 100644
--- a/drivers/st/gpio/stm32_gpio.c
+++ b/drivers/st/gpio/stm32_gpio.c
@@ -15,7 +15,7 @@
 #include <common/bl_common.h>
 #include <common/debug.h>
 #include <drivers/st/stm32_gpio.h>
-#include <drivers/st/stm32mp1_clkfunc.h>
+#include <drivers/st/stm32mp_clkfunc.h>
 #include <lib/mmio.h>
 #include <lib/utils_def.h>