pmic: Extend PMIC framework to support battery related commands

Two extra commands:
"pmic name bat state" and "pmic name bat charge" has been added to
pmic framework. Those provides state display and charge capabilities
to named batteries.

The pmic_core.c file has been refactored to more consistent name scheme.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Stefano Babic <sbabic@denx.de>