arm/dt: msm8974: Only add charger devices for MTP

Liquid platform uses a stack cell charger and implements
its own drivers to supply userspace with information.

Hence disable charger devices by default on PM8941 and enable
it only on necessary platforms such as MTP.

Change-Id: I9d75a9f2a522351df468edaff6adefe31c9fa569
Signed-off-by: David Keitel <dkeitel@codeaurora.org>