mfd: pm8008: Remove driver data structure pm8008_data

Maintaining a local driver data structure that is never shared
outside of the core device is an unnecessary complexity.  Half of the
attributes were not used outside of a single function, one of which
was not used at all.  The remaining 2 are generic and can be passed
around as required.

Signed-off-by: Lee Jones <lee.jones@linaro.org>