MIPS: Refactor boot and boot/compressed rules

Split out the arch/mips/boot/ and arch/mips/boot/compressed/ targets
into boot-y and bootz-y variables. This makes it slightly cleaner to add
new targets.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5793/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Makefile

@@ -254,6 +254,17 @@ drivers-$(CONFIG_OPROFILE)	+= arch/mips/oprofile/
 # suspend and hibernation support
 drivers-$(CONFIG_PM)	+= arch/mips/power/
 
+# boot image targets (arch/mips/boot/)
+boot-y			:= vmlinux.bin
+boot-y			+= vmlinux.ecoff
+boot-y			+= vmlinux.srec
+
+# compressed boot image targets (arch/mips/boot/compressed/)
+bootz-y			:= vmlinuz
+bootz-y			+= vmlinuz.bin
+bootz-y			+= vmlinuz.ecoff
+bootz-y			+= vmlinuz.srec
+
 ifdef CONFIG_LASAT
 rom.bin rom.sw: vmlinux
 	$(Q)$(MAKE) $(build)=arch/mips/lasat/image $@
@@ -280,11 +291,11 @@ vmlinux.64: vmlinux
 all:	$(all-y)
 
 # boot
-vmlinux.bin vmlinux.ecoff vmlinux.srec: $(vmlinux-32) FORCE
+$(boot-y): $(vmlinux-32) FORCE
 	$(Q)$(MAKE) $(build)=arch/mips/boot VMLINUX=$(vmlinux-32) arch/mips/boot/$@
 
 # boot/compressed
-vmlinuz vmlinuz.bin vmlinuz.ecoff vmlinuz.srec: $(vmlinux-32) FORCE
+$(bootz-y): $(vmlinux-32) FORCE
 	$(Q)$(MAKE) $(build)=arch/mips/boot/compressed \
 	   VMLINUX_LOAD_ADDRESS=$(load-y) 32bit-bfd=$(32bit-bfd) $@