C2SoftHevcEnc: Do not initialize encoder in onInit()

Like c2 soft avc encoder, defer encoder initialization to process()
This change allows multiple start() and reset() calls.

Test: adb shell /data/local/tmp/vts/VtsHidlC2V1_0TargetComponentTest\
 -C c2.android.hevc.encoder -P /sdcard/media/ -I software
Test: atest android.media.cts.VideoEncoderTest
Bug: 133067331

Change-Id: Ia66206e9cfc008508222900dc498ff3b30e2fb4e