stm32mp: add soc.c file

Add a new file soc.c for common functions between stm32mp1 and stm32mp2
family and move print_cpuinfo() in this new file.

Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@foundries.io>
diff --git a/arch/arm/mach-stm32mp/Makefile b/arch/arm/mach-stm32mp/Makefile
index 00dc25b..fdcbbf9 100644
--- a/arch/arm/mach-stm32mp/Makefile
+++ b/arch/arm/mach-stm32mp/Makefile
@@ -6,6 +6,7 @@
 obj-y += dram_init.o
 obj-y += syscon.o
 obj-y += bsec.o
+obj-y += soc.o
 
 obj-$(CONFIG_STM32MP15x) += stm32mp1/
 obj-$(CONFIG_STM32MP13x) += stm32mp1/