mmc: remove hc_wp_grp_size from struct mmc if not needed

hc_wp_grp_size is needed only if hardware partitionning is used.
On ARM removing it saves about 30 bytes of code space.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
diff --git a/include/mmc.h b/include/mmc.h
index cd068b9..a46eaed 100644
--- a/include/mmc.h
+++ b/include/mmc.h
@@ -589,7 +589,9 @@
 	uint write_bl_len;
 	uint erase_grp_size;	/* in 512-byte sectors */
 #endif
+#if CONFIG_IS_ENABLED(MMC_HW_PARTITIONING)
 	uint hc_wp_grp_size;	/* in 512-byte sectors */
+#endif
 #if CONFIG_IS_ENABLED(MMC_WRITE)
 	struct sd_ssr	ssr;	/* SD status register */
 #endif