e_config,e_comp_wl_capture: Add configuration value for video capture.

e_config,e_comp_wl_capture: Add configuration value for video capture.

A variable 'save_video_buffer' is added for configuration of video
capture feature.
Some platform has to set it zero for disabling this feature.

The reason for introducing this is as follow:
On some platform, a video client doesn't present its image buffer,
but present something like dummy buffer having meta information to display
server. Thus, it doesn't make any sense to save this kind of buffer as an
image file, and it can even cause crash like SIGSEGV.
For this reason, this has to be disabled on such platform.

Change-Id: I1b4cc97a41065f6fb8fb36bb42d500fd143ea97a