MIPS: Fix build error for uncompressed non-plain vmlinux kernels

Seen on rm200_defconfig for example:

  CC      arch/mips/boot/compressed/decompress.o
/home/ralf/src/linux/upstream-linus/arch/mips/boot/compressed/decompress.c: In function ‘decompress_kernel’:
/home/ralf/src/linux/upstream-linus/arch/mips/boot/compressed/decompress.c:116: error: implicit declaration of function ‘decompress’
make[3]: *** [arch/mips/boot/compressed/decompress.o] Error 1
make[2]: *** [vmlinuz.ecoff] Error 2
make[1]: *** [sub-make] Error 2
make: *** [all] Error 2

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Makefile

@@ -184,6 +184,15 @@ libs-$(CONFIG_CFE)		+= arch/mips/fw/cfe/
 libs-$(CONFIG_SNIPROM)		+= arch/mips/fw/sni/
 libs-y				+= arch/mips/fw/lib/
 
+#
+# Kernel compression
+#
+ifdef SYS_SUPPORTS_ZBOOT
+COMPRESSION_FNAME		= vmlinuz
+else
+COMPRESSION_FNAME		= vmlinux
+endif
+
 #
 # Board-dependent options and extra files
 #
@@ -344,7 +353,7 @@ load-$(CONFIG_LEMOTE_MACH2F) +=0xffffffff80200000
 core-$(CONFIG_MIPS_MALTA)	+= arch/mips/mti-malta/
 cflags-$(CONFIG_MIPS_MALTA)	+= -I$(srctree)/arch/mips/include/asm/mach-malta
 load-$(CONFIG_MIPS_MALTA)	+= 0xffffffff80100000
-all-$(CONFIG_MIPS_MALTA)	:= vmlinuz.bin
+all-$(CONFIG_MIPS_MALTA)	:= $(COMPRESSION_FNAME).bin
 
 #
 # MIPS SIM
@@ -594,7 +603,7 @@ load-$(CONFIG_SNI_RM)		+= 0xffffffff80600000
 else
 load-$(CONFIG_SNI_RM)		+= 0xffffffff80030000
 endif
-all-$(CONFIG_SNI_RM)		:= vmlinuz.ecoff
+all-$(CONFIG_SNI_RM)		:= $(COMPRESSION_FNAME).ecoff
 
 #
 # Common TXx9