modules/wrc_core/wrc_periph: I2C HIGH init value

Hi,

this is our first MR in preparation for supporting Xilinx/AMD dev boards with White Rabbit. This MR initializes the I2C output registers with 1 to force high-impedance state at bootup. On these dev boards, most I2C peripherals are accessible from both PS and PL. As the idle level of I2C is a logic high, the PL "locks" the bus when the line is pulled low permanently, thus preventing the peripherals from being accessed by the PS.