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/plat/st/stm32mp1/platform.mk b/plat/st/stm32mp1/platform.mk
index 1c5f627..3e34601 100644
--- a/plat/st/stm32mp1/platform.mk
+++ b/plat/st/stm32mp1/platform.mk
@@ -50,6 +50,7 @@
 				drivers/delay_timer/delay_timer.c			\
 				drivers/delay_timer/generic_delay_timer.c		\
 				drivers/st/bsec/bsec.c					\
+				drivers/st/clk/stm32mp_clkfunc.c			\
 				drivers/st/clk/stm32mp1_clk.c				\
 				drivers/st/clk/stm32mp1_clkfunc.c			\
 				drivers/st/ddr/stm32mp1_ddr_helpers.c			\