[media] r820t: Add a tuner driver for Rafael Micro R820T silicon tuner

This driver was written from scratch, based on an existing driver
that it is part of rtl-sdr git tree, released under GPLv2:
	https://groups.google.com/forum/#!topic/ultra-cheap-sdr/Y3rBEOFtHug
	https://github.com/n1gp/gr-baz
	http://cgit.osmocom.org/rtl-sdr/plain/src/tuner_r820t.c
	(there are also other variants of it out there)
>From what I understood from the threads, the original driver was converted
to userspace from a Realtek tree. I couldn't find the original tree.
However, the original driver look awkward on my eyes. So, I decided to
write a new version from it from the scratch, while trying to reproduce
everything found there.
TODO:
- After locking, the original driver seems to have some routines to
  improve reception. This was not implemented here yet.
- RF Gain set/get is not implemented.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Tested-by: Antti Palosaari <crope@iki.fi>

drivers/media/tuners/Kconfig

@@ -248,4 +248,11 @@ config MEDIA_TUNER_IT913X
 	default m if !MEDIA_SUBDRV_AUTOSELECT
 	help
 	  ITE Tech IT913x silicon tuner driver.
+
+config MEDIA_TUNER_R820T
+	tristate "Rafael Micro R820T silicon tuner"
+	depends on MEDIA_SUPPORT && I2C
+	default m if !MEDIA_SUBDRV_AUTOSELECT
+	help
+	  Rafael Micro R820T silicon tuner driver.
 endmenu

drivers/media/tuners/Makefile

@@ -35,6 +35,7 @@ obj-$(CONFIG_MEDIA_TUNER_FC0011) += fc0011.o
 obj-$(CONFIG_MEDIA_TUNER_FC0012) += fc0012.o
 obj-$(CONFIG_MEDIA_TUNER_FC0013) += fc0013.o
 obj-$(CONFIG_MEDIA_TUNER_IT913X) += tuner_it913x.o
+obj-$(CONFIG_MEDIA_TUNER_R820T) += r820t.o
 
 ccflags-y += -I$(srctree)/drivers/media/dvb-core
 ccflags-y += -I$(srctree)/drivers/media/dvb-frontends