mmc: core: new discard feature support at eMMC v4.5

MMC v4.5 supports the DISCARD feature (CMD38).  It's different from
trim and there's no check bit.  Currently it's only supported at v4.5.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
index 711c3f8..5513785 100644
--- a/include/linux/mmc/card.h
+++ b/include/linux/mmc/card.h
@@ -80,6 +80,9 @@
 	u8			raw_sec_feature_support;/* 231 */
 	u8			raw_trim_mult;		/* 232 */
 	u8			raw_sectors[4];		/* 212 - 4 bytes */
+
+	unsigned int            feature_support;
+#define MMC_DISCARD_FEATURE	BIT(0)                  /* CMD38 feature */
 };
 
 struct sd_scr {