make: move cpu specific CFLAGS into cpu makefile

boards/Makefile.include.cortex_common

@@ -5,12 +5,6 @@ include $(RIOTBOARD)/Makefile.include.gnu
 # use cortex name of CPU folder, but enable board Makefile to override
 export MCPU ?= $(CORTEX)
 
-#
-# CPU model specifics
-ifeq ($(CORTEX),cortex-m4)
-CFLAGS_FPU += -mfloat-abi=hard -mfpu=fpv4-sp-d16
-endif
-
 # define build specific options
 export CFLAGS_CPU   = -mcpu=$(MCPU) -mlittle-endian -mthumb -mno-thumb-interwork $(CFLAGS_FPU)
 export CFLAGS_STYLE = -std=gnu99 -Wall -Wstrict-prototypes

cpu/Makefile.include.cortex_common

 # This CPU implementation is using the new core/CPU interface:
 export CFLAGS += -DCOREIF_NG=1
 
+# CPU model specifics
+ifeq ($(CORTEX),cortex-m4)
+export CFLAGS_FPU += -mfloat-abi=hard -mfpu=fpv4-sp-d16
+endif
+
 # Tell the build system that the CPU depends on the Cortex-M common files:
 export USEMODULE += $(CORTEX)_common