v4l2_codec2 encoder: Add missing support for LEVEL_AVC_4_2.

Currently the C2Config::LEVEL_AVC_4_2 level is not advertised as
supported value for the C2_PARAMKEY_PROFILE_LEVEL parameter. This
causes the V4L2 encoder to use the next supported level LEVEL_AVC_5,
making the EncoderProfileLevelTest#testValidateProfileLevel CTS test
fail.

BUG: 188415875
Test: EncoderProfileLevelTest#testValidateProfileLevel
Change-Id: Ifd5caa6d70c592a7379260876600b075432ac7d8