RFC power: supply: qcom_fg: remove PMI8994 fuel gauge

Remove Pre-Gen3 fuel gauge support the two generation have very little in common. This driver squashing 2 driver together so better to separate them.

NOTE: I don't have any sdm845 device so i have not tested it, it is compiling without warnings. Maybe i can check on sdm660.

The driver separation idea comes from @Tooniis

TODO:

• Check for leftovers
• Maybe driver should be renamed to qcom-pmi8998-fg