libstagefright: use appropriate hevc decoder on 8916 and 8939

8916 supports HEVC s/w decoder and 8939 supports h/w decoder.
Based on media.swhevccodectype property value, Add appropriate
HEVC decoder to the MediaCodecList.

Change-Id: I06a522fee4e54a75555f2b55e03addcace643d9d