staging: ste_rmi4: kill platform_data hack

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.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>