power: pm8921-charger: report DC online for some platforms

Some hardware platforms can supply VPH_PWR without battery
or charger being present.

To avoid shutting down due to no connected power sources
from the perspective of software set a flag that forces
the DC supply to be online for this type of platform.

Change-Id: I325ea00d2103da229bfb7a854ebb7f7fd556c16b
Signed-off-by: David Keitel <dkeitel@codeaurora.org>