Improve input devices changed logs

Currently, "reconfiguring input devices" log is hard to read, because it
dumps the values as hex. That means, the reader has to go into code to
understand what the actual changes are. Furthermore, if the defines are
added/removed/modified between releases, it's even harder to debug. To
improve this, convert to the actual values before printing.

This will also help confirm that these are only ever invoked with a
single change. Maybe we can change to enum class then.

Bug: 137212522
Test: adb logcat | grep -i "input devices"
Change-Id: I6b40d1c785df8a57c9e2619210906d326844d69d
Before: InputReader: Reconfiguring input devices.  changes=0x00000010
After: InputReader: Reconfiguring input devices, changes=KEYBOARD_LAYOUTS |