c2_e2e_test: Add fake renderer

This change adds an option to use a fake renderer when decoding. The
fake renderer allows the decoder to operate with realistic frame timings
while avoiding an actual dependency on the display stack.

The change also fixes an overflow issue in a log statement.

Bug: None
Test: manually test new option

Change-Id: Id10809c98584d3df390dea068307e32d6afd469b