ARM: dts: stm32mp15: remove clksrc include in SCMI dtsi file

The include file stm32mp1-clksrc.h is not necessary for the SCMI STM32MP15
dtsi files as the clock tree is not defined in the U-Boot SCMI device tree;
these SCMI device tree only support TFABOOT with stm32mp15_defconfig,
SPL with the basic boot defconfig is not supported.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>