docs: ABI: sysfs-class-power: unify duplicated properties

The ABI is not supposed to have duplicated entries, as warned
by get_abi.pl:

	$ ./scripts/get_abi.pl validate 2>&1|grep sysfs-class-power
	Warning: /sys/class/power_supply/<supply_name>/current_avg is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:108  Documentation/ABI/testing/sysfs-class-power:391
	Warning: /sys/class/power_supply/<supply_name>/current_max is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:121  Documentation/ABI/testing/sysfs-class-power:404
	Warning: /sys/class/power_supply/<supply_name>/current_now is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:130  Documentation/ABI/testing/sysfs-class-power:414
	Warning: /sys/class/power_supply/<supply_name>/temp is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:281  Documentation/ABI/testing/sysfs-class-power:493
	Warning: /sys/class/power_supply/<supply_name>/temp_alert_max is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:291  Documentation/ABI/testing/sysfs-class-power:505
	Warning: /sys/class/power_supply/<supply_name>/temp_alert_min is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:306  Documentation/ABI/testing/sysfs-class-power:521
	Warning: /sys/class/power_supply/<supply_name>/temp_max is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:322  Documentation/ABI/testing/sysfs-class-power:537
	Warning: /sys/class/power_supply/<supply_name>/temp_min is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:333  Documentation/ABI/testing/sysfs-class-power:547
	Warning: /sys/class/power_supply/<supply_name>/voltage_max is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:356  Documentation/ABI/testing/sysfs-class-power:571
	Warning: /sys/class/power_supply/<supply_name>/voltage_min is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:367  Documentation/ABI/testing/sysfs-class-power:581
	Warning: /sys/class/power_supply/<supply_name>/voltage_now is defined 2 times:  Documentation/ABI/testing/sysfs-class-power:378  Documentation/ABI/testing/sysfs-class-power:591

Yet, both USB and Battery share a common set of charging-related
properties.

Unify the entries for such properties in order to avoid
duplication, while preserving the battery and USB-specific
data properly documented.
Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/bcdf5f76326ea48a990a7cac612af216c387537d.1604042072.git.mchehab+huawei@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>