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/Kconfig b/drivers/misc/Kconfig
index 1f69743..3d57adf 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -24,7 +24,8 @@
 	  AD5260, AD5262, AD5263, AD5290, AD5291, AD5292, AD5293,
 	  AD7376, AD8400, AD8402, AD8403, ADN2850, AD5241, AD5242,
 	  AD5243, AD5245, AD5246, AD5247, AD5248, AD5280, AD5282,
-	  ADN2860, AD5273, AD5171, AD5170, AD5172, AD5173
+	  ADN2860, AD5273, AD5171, AD5170, AD5172, AD5173, AD5270,
+	  AD5271, AD5272, AD5274
 	  digital potentiometer chips.
 
 	  See Documentation/misc-devices/ad525x_dpot.txt for the