V4L/DVB (4012): Fix cx24123 diseqc

Rework diseqc support to be more in line with the other demod drivers.
Fix Nova-S-Plus/Nova-SE2 diseqc.
Cleanup API.

Signed-off-by: Andrew de Quincey <adq_dvb@lidskialf.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
diff --git a/drivers/media/video/cx88/Kconfig b/drivers/media/video/cx88/Kconfig
index 6302739..c092d22 100644
--- a/drivers/media/video/cx88/Kconfig
+++ b/drivers/media/video/cx88/Kconfig
@@ -61,6 +61,7 @@
 	select DVB_LGDT330X
 	select DVB_NXT200X
 	select DVB_CX24123
+	select DVB_ISL6421
 	---help---
 	  This builds cx88-dvb with all currently supported frontend
 	  demodulators.  If you wish to tweak your configuration, and
@@ -139,6 +140,7 @@
 	default y
 	depends on VIDEO_CX88_DVB && !VIDEO_CX88_DVB_ALL_FRONTENDS
 	select DVB_CX24123
+	select DVB_ISL6421
 	---help---
 	  This adds DVB-S support for cards based on the
 	  Connexant 2388x chip and the CX24123 demodulator.