mvebu: image: align subtargets makefile names

Align subtargets makefiles names to actual subtargets.

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>
Acked-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/mvebu/image/Makefile

@@ -118,15 +118,15 @@ define Device/NAND-512K
 endef
 
 ifeq ($(SUBTARGET),cortexa9)
-include cortex-a9.mk
+include cortexa9.mk
 endif
 
 ifeq ($(SUBTARGET),cortexa53)
-include cortex-a53.mk
+include cortexa53.mk
 endif
 
 ifeq ($(SUBTARGET),cortexa72)
-include cortex-a72.mk
+include cortexa72.mk
 endif
 
 $(eval $(call BuildImage))