Revert troublesome ath_hal config definitions back to the original.

This means that, under the new config(1) modular build, if the option
ATHHAL_AR5210, that extends the ath driver to support AR5210, is selected,
the relevant 10 ar5210_*.c files end up being embedded into the "netbsd.ko"
module, which is pretty much opposite of modularity.

(uebayasi)