power: pm8921-charger: support battery less hardware

There are hardware configurations where a battery is not present. Such
hardware runs from a external power adapter.

Do not invoke BMS api for reporting charge percentage instead report
100%. Also report a favourable battery temperature.

Change-Id: I4f14b7419f7a90813650601638f6563422c13ae4
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>