mfd: Add tps65921 support from twl-core

Very similar to TPS65920
List of differences: http://www.ti.com/litv/pdf/swcu066bSigned-off-by: NOleg Drokin <green@linuxhacker.ru>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

drivers/mfd/twl-core.c

@@ -1283,6 +1283,8 @@ static const struct i2c_device_id twl_ids[] = {
 	{ "tps65950", 0 },		/* catalog version of twl5030 */
 	{ "tps65930", TPS_SUBSET },	/* fewer LDOs and DACs; no charger */
 	{ "tps65920", TPS_SUBSET },	/* fewer LDOs; no codec or charger */
+	{ "tps65921", TPS_SUBSET },	/* fewer LDOs; no codec, no LED
+					   and vibrator. Charger in USB module*/
 	{ "twl6030", TWL6030_CLASS },	/* "Phoenix power chip" */
 	{ "twl6025", TWL6030_CLASS | TWL6025_SUBCLASS }, /* "Phoenix lite" */
 	{ /* end of list */ },