matroskamux: add support for writing CRC32 checksums

Submitted by surendra

Link to original bug (#731821)

Description

I am able to record the IP camera H264 stream in to MKV file by using the below
pipe line.

gst-launch-1.0 -e rtspsrc
location="rtsp://10.33.15.1:554/udpstream_ch1_stream1" ! rtph264depay !
h264parse ! matroskamux ! filesink location=test1.mkv

I am able to play the recorded file with any MKV (h264)compatible player.
I am checking the recorded MKV file EBML tree using AVI MUX GUI
application(Picture attached).

recorded.png

As per the specification of EMBL MKV file also should contain the CRC32 for the
parent filed(see the spec piture attached).

Recorded MKV file is missing CRC32 elements.

Reference discussion :
http://gstreamer-devel.966125.n4.nabble.com/MKV-file-in-EMBL-Tree-View-CRC32-is-missing-td4667472.html