KM: define CONFIG_SYS_I2C_INIT_BOARD only for concerned board

This must be defined for all the keymile boards that use the common
i2c_abort function that is used to "reset" the I2C bus. These are
currently km82xx and km_arm boards.

The  km83xx boards use other functions and thus do not need this.

This patch removes the CONFIG_SYS_I2C_INIT_BOARD from keymile-common.h
and defines it for km_arm.h and km82xx.h.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>