v4l2_codec2: Split off H264 V4L2 configuration to separate function.

This CL performs a small bit of cleanup, splitting all H.264-related
V4L2 device configuration into a separate function.

Bug: 143333813
Test: arc.VideoEncodeAccel.h264_192p_i420_vm
Change-Id: I8304294d9424ff6d1f38bffd509051b25cc1a64b