gzip/zlib: make features optional

If you really want to slim down U-Boot and you would rather use a higher
compression scheme (like LZMA), it'd be nice to disable gzip/zlib since
these code bases take up a significant amount of space.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/lib_generic/Makefile b/lib_generic/Makefile
index 4e4496a..c45f07c 100644
--- a/lib_generic/Makefile
+++ b/lib_generic/Makefile
@@ -37,7 +37,7 @@
 COBJS-y += ctype.o
 COBJS-y += display_options.o
 COBJS-y += div64.o
-COBJS-y += gunzip.o
+COBJS-$(CONFIG_GZIP) += gunzip.o
 COBJS-$(CONFIG_LMB) += lmb.o
 COBJS-y += ldiv.o
 COBJS-$(CONFIG_MD5) += md5.o
@@ -48,7 +48,7 @@
 COBJS-y	+= strmhz.o
 COBJS-y += time.o
 COBJS-y += vsprintf.o
-COBJS-y += zlib.o
+COBJS-$(CONFIG_ZLIB) += zlib.o
 COBJS-$(CONFIG_RBTREE)	+= rbtree.o
 
 COBJS	:= $(COBJS-y)