mmc: core: Add helper function for EXT_CSD support

The helper function mmc_can_ext_csd() will return a positive value if
the card supports the EXT_CSD register. Start using it at relavant
places in the mmc core.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 5226ef8..7c257c9 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -190,7 +190,7 @@
 
 	*new_ext_csd = NULL;
 
-	if (card->csd.mmca_vsn < CSD_SPEC_VER_4)
+	if (!mmc_can_ext_csd(card))
 		return 0;
 
 	/*
@@ -852,7 +852,7 @@
 	int err, ddr;
 
 	/* Power class selection is supported for versions >= 4.0 */
-	if (card->csd.mmca_vsn < CSD_SPEC_VER_4)
+	if (!mmc_can_ext_csd(card))
 		return 0;
 
 	bus_width = host->ios.bus_width;
@@ -913,7 +913,7 @@
 	unsigned idx, bus_width = 0;
 	int err = 0;
 
-	if ((card->csd.mmca_vsn < CSD_SPEC_VER_4) &&
+	if (!mmc_can_ext_csd(card) &&
 	    !(host->caps & (MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA)))
 		return 0;
 
@@ -1154,7 +1154,7 @@
 {
 	int err = 0;
 
-	if (card->csd.mmca_vsn < CSD_SPEC_VER_4)
+	if (!mmc_can_ext_csd(card))
 		goto bus_speed;
 
 	if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200)