Add logging when attempting to dream from power press.

Added a log statement to the logic that attempts to dream from a short
power press in order to identify black screen situations caused by an
inability to start dreaming (likely because the system thinks it is
already dreaming).

Bug: 282191629
Test: manually by pushing the power button when the device is already
dreaming and seeing that the log statement is emitted.

Change-Id: I2b18715677ba14c82694adf7480cbed1e8862231