clk: stm32mp1: pm for clock under secure RCC registers

When RCC[TZEN] is enabled secure world needs to save the secure and
non-secure clock configuration settings and restore them when
resuming.

Function stm32mp1_clk_mpu_suspend()/stm32mp1_clk_mpu_resume() are
made local and renamed clk_mpu_suspend()/clk_mpu_resume(). The
overall clock configuration is saved with stm32mp1_clock_suspend()
and restored with stm32mp1_clock_resume().

Change-Id: I1fc0c693c59ffe972961c2b23f30a39a520f3aaa
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>