i2c: add nexell driver

Changes in relation to FriendlyARM's U-Boot nanopi2-v2016.01:
- i2c/nx_i2c.c: Some adaptions mainly because of changes in
  "struct udevice".
- several Bugfixes in nx_i2c.c.
- the driver has been for s5p6818 only. Code extended appropriately
  in order s5p4418 is also working.
- "probe_chip" added.
- pinctrl-driver/dt is used instead of configuring the i2c I/O-pins
  in the i2c-driver.
- '#ifdef CONFIG...' changed to 'if (IS_ENABLED(CONFIG...))' where
  possible (and similar).
- livetree API (dev_read_...) is used instead of fdt one (fdt...).

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>
diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index 87d11b6..dec6dc9 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -333,6 +333,15 @@
 	 MXC I2C8 Slave
 endif
 
+config SYS_I2C_NEXELL
+	bool "Nexell I2C driver"
+	depends on DM_I2C
+	help
+	  Add support for the Nexell I2C driver. This is used with various
+	  Nexell parts such as S5Pxx18 series SoCs. All chips
+	  have several I2C ports and all are provided, controlled by the
+	  device tree.
+
 config SYS_I2C_OMAP24XX
 	bool "TI OMAP2+ I2C driver"
 	depends on ARCH_OMAP2PLUS || ARCH_K3