mfd: Add support for stmpe variant 610

STMPE610 is very much like STMPE811, except the number of gpio pins, which is 8
in 811 and 6 in 610. This patch adds support for variant 610. STMPE610 will
share most of the code with STMPE811.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/stmpe-i2c.c b/drivers/mfd/stmpe-i2c.c
index 0a43659..b11d33b 100644
--- a/drivers/mfd/stmpe-i2c.c
+++ b/drivers/mfd/stmpe-i2c.c
@@ -71,6 +71,7 @@
 }
 
 static const struct i2c_device_id stmpe_i2c_id[] = {
+	{ "stmpe610", STMPE610 },
 	{ "stmpe811", STMPE811 },
 	{ "stmpe1601", STMPE1601 },
 	{ "stmpe2401", STMPE2401 },