fuel_gauge: Join get/set prop structs

The fuel gauge API uses separate get/set property structs to indicate what
properties are readable or writable. This lead to duplication in property
names and potential confusion for new users of the API. See issue #61818.
In addition to above, drivers already determine at runtime if a property is
supported for read or write actions.

Join the get/set fuel gauge property structs as a single struct.

Signed-off-by: Aaron Massey <aaronmassey@google.com>