power: qpnp-charger: don't allow ULPM usage when charging disabled

Some platforms do not have the battery interface
peripheral initialized. This may result in an
unauthorized access to a PMIC register with
offset 0 and cause the device to crash.

Fix this by not allowing the usage of ULPM for
boards that do not have the bat_if_base address
initialized or in which chip->charging_disabled is set.

Change-Id: I055451bfd1b2f7eb535e57e68a21d6ded41f0a55
Signed-off-by: David Keitel <dkeitel@codeaurora.org>