drivers/misc/ad525x_dpot.c: new features

Add support for AD5270, AD5271, AD5272, AD5274 digital potentiometers.
Add 20-TP feature for AD5291 and AD5292 parts, and update feature list.
AD5291 rdac read back must be shifted by two.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Chris Verges <chrisv@cyberswitching.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/misc/ad525x_dpot-spi.c b/drivers/misc/ad525x_dpot-spi.c
index 6cfcb63..7f9a55a 100644
--- a/drivers/misc/ad525x_dpot-spi.c
+++ b/drivers/misc/ad525x_dpot-spi.c
@@ -38,6 +38,8 @@
 	{.name = "ad8402", .devid = AD8402_ID},
 	{.name = "ad8403", .devid = AD8403_ID},
 	{.name = "adn2850", .devid = ADN2850_ID},
+	{.name = "ad5270", .devid = AD5270_ID},
+	{.name = "ad5271", .devid = AD5271_ID},
 	{}
 };