arm/dt: msm-pm8019: Add power key support

PMIC8019 supports QPNP PON (Power ON) module
to provide the functionalities like power on/off
reason, key press/release, reset configuration
and various other PON specific features. Add support
for power key which is connected to physical CBLPWR pin.

Change-Id: If9eb74b1d745a42384ef9c9af3524626408e7bea
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>