arm: mvebu: a3720: Create Kconfig option for I2C_MV

Move the config option CONFIG_I2C_MV to a Kconfig option
CONFIG_SYS_I2C_MV and move the default definition from config header
files into defconfigs.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/turris_mox_defconfig b/configs/turris_mox_defconfig
index e494aeb..3cae32f 100644
--- a/configs/turris_mox_defconfig
+++ b/configs/turris_mox_defconfig
@@ -61,6 +61,7 @@
 CONFIG_CLK_MVEBU=y
 # CONFIG_MVEBU_GPIO is not set
 CONFIG_DM_I2C=y
+CONFIG_SYS_I2C_MV=y
 CONFIG_LED=y
 CONFIG_LED_GPIO=y
 CONFIG_MISC=y