Input: gameport - add helper macro for gameport_driver boilerplate

This patch introduces the module_gameport_driver macro which is a
convenience macro for gameport driver modules similar to
module_platform_driver. It is intended to be used by drivers
which init/exit section does nothing but registers/unregisters the
gameport driver. By using this macro it is possible to eliminate a
few lines of boilerplate code per gameport driver.

Based on work done by Lars-Peter Clausen <lars@metafoo.de> for
other buses (i2c and spi).

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>