lpbin: Add mute property
lpbin: Add mute property

Regardless presence of audio stream, mute property
can turn off audio forcedly. In addition, the upper
layer can control audio status via 'mute' property.

:Issued Address:
[GF-22105]: Audio should be off when trick play(under x2)
            in case using 'audioOutput' option off

Change-Id: Ie3a894dad22292a5d0b53e8e3e38d0a1c8b38155
Reviewed-on: https://gpro.palm.com/11768
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Reviewed-by: Wonchul Lee <9841bdbec9dbb2acc2dcaaa1dab0491399f0e464@lge.com>
Reviewed-by: HoonHee Lee <41497318ef67053f37c2ac0e974a3369f66d66ec@lge.com>
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

justinjoy/gst-plugins-lp,justinjoy/gst-plugins-lp