The old code allowed each target to specify its adc targets but this proved
useless since the target rely directly on imx233/lradc for input method and
generic adc is mostly used for battery and debug. Remove all target specific
files and provide a generic implemenation. The targets can still specify a
battery temperature channel in powermgmt-target.h
Change-Id: I68cf2e3e46379d174ac6d774ffb237bb15a19ae3
