Rework Apple SMC attachment goo and split into multiple modules.

The four modules are apple_smc for the core functions, apple_smc_acpi
for attachment at acpi, and apple_smc_fan & apple_smc_temp for stuff
on the SMC.

Seems like there's a lot more bookkeeping necessary to maintain
children of an applesmc device implemented by loadable modules.
Maybe there's a better way I just haven't figured out yet.

(riastradh)