eeepc-laptop: pull out SENSOR_STORE_FUNC and SENSOR_SHOW_FUNC macros

Pull out EEEPC_SENSOR_STORE_FUNC and EEEPC_SENSOR_SHOW_FUNC. These
macros define functions that call store_sys_hwmon() and show_sys_hwmon()
respectively. This helps prevent duplication later on.

Signed-off-by: Frans Klaver <fransklaver@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>