cpu: use cortexm common linkerscript

cpu/lpc1768/ldscripts/lpc1768.ld

cpu/nrf51822/ldscripts/nrf51822qfaa.ld

cpu/sam3x8e/ldscripts/sam3x8e.ld

cpu/samd21/ldscripts/samr21g18a.ld

cpu/saml21/ldscripts/saml21j18a.ld

cpu/stm32f0/ldscripts/stm32f051r8.ld

cpu/stm32f0/ldscripts/stm32f091rc.ld

cpu/stm32f1/ldscripts/stm32f103cb.ld

cpu/stm32f1/ldscripts/stm32f103re.ld

cpu/stm32f3/ldscripts/stm32f303vc.ld

cpu/stm32f3/ldscripts/stm32f334r8.ld

cpu/stm32f4/ldscripts/stm32f407vg.ld

cpu/stm32f4/ldscripts/stm32f415rg.ld

cpu/stm32l1/ldscripts/stm32l152ret6.ld