ab8500_bm: Rename battery management platform data to something more logical

The platform specific battery management configuration data structure
is currently called 'bat' short for 'battery'; however, it contains
information for all components of the battery management group, rather
than information pertaining to the battery itself - there are other
structures for that. So, in keeping with its structure namesake
'abx500_bm_data', we rename it to 'bm' here. Using similar logic,
we're also renaming 'bmdevs_of_probe' to the more device specific
'ab8500_bm_of_probe'.

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