disk/part.c: Make features optional

If we don't want to build support for any partition types we can now
add #undef CONFIG_PARTITIONS in a board config file to keep this from
being compiled in. Otherwise boards assume this is compiled in by
default

Signed-off-by: Matthew McClintock <msm@freescale.com>
diff --git a/disk/Makefile b/disk/Makefile
index 17266a2..5affe34 100644
--- a/disk/Makefile
+++ b/disk/Makefile
@@ -27,7 +27,7 @@
 
 LIB	= $(obj)libdisk.o
 
-COBJS-y += part.o
+COBJS-$(CONFIG_PARTITIONS) 	+= part.o
 COBJS-$(CONFIG_MAC_PARTITION)   += part_mac.o
 COBJS-$(CONFIG_DOS_PARTITION)   += part_dos.o
 COBJS-$(CONFIG_ISO_PARTITION)   += part_iso.o