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/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index cbd7567..7e703c0 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -1167,12 +1167,14 @@
 	return 0;
 }
 
+#ifdef CONFIG_PARTITIONS
 block_dev_desc_t *mmc_get_dev(int dev)
 {
 	struct mmc *mmc = find_mmc_device(dev);
 
 	return mmc ? &mmc->block_dev : NULL;
 }
+#endif
 
 int mmc_init(struct mmc *mmc)
 {