mfd: retu: Add Tahvo support

Tahvo is a multi-function device on Nokia 770, implementing USB
transceiver and charge/battery control.

It's so close to Retu that a single driver can support both.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 2f3ce18..9de0502 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -371,13 +371,13 @@
 	  The drivers do not support all features the board exposes.
 
 config MFD_RETU
-	tristate "Nokia Retu multi-function device"
+	tristate "Nokia Retu and Tahvo multi-function device"
 	select MFD_CORE
 	depends on I2C && GENERIC_HARDIRQS
 	select REGMAP_IRQ
 	help
-	  Retu is a multi-function device found on Nokia Internet Tablets
-	  (770, N800 and N810).
+	  Retu and Tahvo are a multi-function devices found on Nokia
+	  Internet Tablets (770, N800 and N810).
 
 config MFD_PCF50633
 	tristate "NXP PCF50633"