iio:filter:admv8818: add support for ADMV8818

The ADMV8818-EP is a fully monolithic microwave integrated
circuit (MMIC) that features a digitally selectable frequency of
operation. The device features four independently controlled high-
pass filters (HPFs) and four independently controlled low-pass
filters (LPFs) that span the 2 GHz to 18 GHz frequency range.

Datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/admv8818-ep.pdf
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>

drivers/iio/filter/Kconfig

@@ -5,4 +5,14 @@
 
 menu "Filters"
 
+config ADMV8818
+	tristate "Analog Devices ADMV8818 High-Pass and Low-Pass Filter"
+	depends on SPI && COMMON_CLK && 64BIT
+	help
+	  Say yes here to build support for Analog Devices ADMV8818
+	  2 GHz to 18 GHz, Digitally Tunable, High-Pass and Low-Pass Filter.
+
+	  To compile this driver as a module, choose M here: the
+	  modiule will be called admv8818.
+
 endmenu

drivers/iio/filter/Makefile

@@ -4,3 +4,4 @@
 #
 
 # When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_ADMV8818) += admv8818.o