power: qpnp-fg: register interrupts last

To avoid race conditions with the power supply framework, only register
interrupts once initialization of spmi nodes and the power supply has
been completed.

Change-Id: I5b0ac1ccac053f5d85890a0951e51efb90aadf06
Signed-off-by: David Keitel <dkeitel@codeaurora.org>