Merge pull request #7799 from kYc0o/factorise_stm32_ld

boards/bluepill/Makefile.include

boards/nucleo-l152/Makefile.include

boards/opencm904/Makefile.include

boards/spark-core/Makefile.include

cpu/stm32_common/Makefile.include

cpu/stm32_common/ldscripts/stm32_common.ld

cpu/stm32_common/stm32_mem_lengths.mk

cpu/stm32f0/ldscripts/stm32f030r8.ld

cpu/stm32f0/ldscripts/stm32f031k6.ld

cpu/stm32f0/ldscripts/stm32f042k6.ld

cpu/stm32f0/ldscripts/stm32f051r8.ld

cpu/stm32f0/ldscripts/stm32f070rb.ld

cpu/stm32f0/ldscripts/stm32f072rb.ld

cpu/stm32f0/ldscripts/stm32f091rc.ld

cpu/stm32f1/ldscripts/stm32f103c8.ld

cpu/stm32f1/ldscripts/stm32f103c8_bluepill.ld

cpu/stm32f1/ldscripts/stm32f103cb.ld

cpu/stm32f1/ldscripts/stm32f103cb_opencm904.ld

cpu/stm32f1/ldscripts/stm32f103cb_sparkcore.ld

cpu/stm32f1/ldscripts/stm32f103rb.ld