There is only one instance of the platform data for synaptics_i2c_rmi4
in the mainline kernel, so there is no point of pretending its
variable here. The only member that has a dependency on the platform
is actually the interrupt number, and there is a field in the
i2c_client structure that gets initialized from the board info,
so we can trivially move the board_into into the platform without
knowledge of the platform_data structure.