Log the requested display policy.

This way we can track what the general desire for the display is. Note
that this is different than tracking the actual display state since, for
example, you may be applying POLICY_DOZE but the DozeService actually
has the display in the ON state.

Bug: 122949636
Test: manual inspection
Change-Id: I65b7e26937f6fbb40057a49c4ebe4aed7380100b