ab8500_charger: Rename the power_loss function

Rename the ab8500_power_loss_handling function to a more
descriptive name ab8500_enable_disable_sw_fallback

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Robert Marklund <robert.marklund@stericsson.com>
Reviewed-by: Par-Olof HAKANSSON <par-olof.hakansson@stericsson.com>
Reviewed-by: Karl KOMIEROWSKI <karl.komierowski@stericsson.com>
Tested-by: Par-Olof HAKANSSON <par-olof.hakansson@stericsson.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>