mmc: make optional the support for eMMC hardware partitioning

Not all boards have an eMMC and not all users have a need for this.
Allow to compile it out. By default it is still included.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 400e163..67d05c5 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -950,6 +950,7 @@
 	return ret;
 }
 
+#if CONFIG_IS_ENABLED(MMC_HW_PARTITIONING)
 int mmc_hwpart_config(struct mmc *mmc,
 		      const struct mmc_hwpart_conf *conf,
 		      enum mmc_hwpart_conf_mode mode)
@@ -1143,6 +1144,7 @@
 
 	return 0;
 }
+#endif
 
 #if !CONFIG_IS_ENABLED(DM_MMC)
 int mmc_getcd(struct mmc *mmc)