power_supply: bq27xxx_battery: Group register mappings into one table

Currently for each device with a unique register map we have a named
array that we then merge into a multidimensional array. Skip this
middle step and apply the register arrays directly to the multi-array.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>