mmc: core: add support for eMMC Dual Data Rate

eMMC voltage change not required for 1.8V.  3.3V and 1.8V vcc
are capable of doing DDR. vccq of 1.8v is not required.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Reviewed-by: Arindam Nath <arindam.nath@amd.com>
Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 6716bd1..de32e6a 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -66,6 +66,7 @@
 
 #define MMC_SIGNAL_VOLTAGE_330	0
 #define MMC_SIGNAL_VOLTAGE_180	1
+#define MMC_SIGNAL_VOLTAGE_120	2
 
 	unsigned char	drv_type;		/* driver type (A, B, C, D) */